Slark
* Slark's dependence on Pounce and close range makes him very easy to hit with 
Purification and 
Hammer of Purity.
* Slark's damage, even with a high count of Essence Shift stacks, is easily negated by Omniknight's heals and 
Guardian Angel.
Legion Commander
* Purification prevents Legion Commander from killing her target, and will always hit her during Duels.
* Guardian Angel completely wastes Duel's duration and can save an ally across the map when upgraded with 
Aghanim's Scepter.
Additional:
* Both Guardian Angel and Purification are perfect counters against 
Duel.
Slark
* 
Nether Blast will still hit Slark even if he is hidden during Shadow Dance.
* Even though Pugna can rarely target Slark directly with 
Decrepify, he can still use it defensively on an ally to prevent Slark from getting stacks.
* Despite being somewhat easy to break with Pounce, Pugna can damage Slark and provide vision over him with 
Life Drain.
Legion Commander
* Decrepify on either hero stops Legion Commander from completing a Duel, and dissuades her from initiating Duels on ethereal allies.
* Life Drain can help Pugna's teammates win a fight, either by killing Legion Commander or replenishing her target's health.
Additional:
* Decrepify prevents Legion Commander from attacking allies during Duel, regardless if it's used on her or on the ally .
* Pugna can easily cast Decrepify, Nether Blast and Life Drain on Legion during the 4/4.75/5.5/8 seconds of duel
Slark
* Heroes that can deny Slark early kills will prevent him from snowballing: 
Dazzle, 
Abaddon.
Legion Commander
* If he isn't broken (break), Abaddon can use Borrowed Time to waste Legion Commander's Duel, As Borrowed Time has a shorter cooldown, Legion Commander can't win duels, effectively reducing her targets by one, Duel also means that Borrowed Time heals Abaddon for the duration of the duel, as Legion can't stop attacking.
Additional:
* 
Aphotic Shield and 
Mist Coil makes it hard for Legion Commander to kill Abaddon's teammates in Duels.
* 
Borrowed Time makes Abaddon nearly impossible to kill in Duels, and often replenishes much of his health because Legion Commander cannot manually stop attacking during Duels.
Slark
* 
Slark's Dark Pact and Pounce can deny only one Earthbind and Poof can penetrate Shadow Dance if he doesn't build Black King Bar.
Additional:
* 
Earthbind and 
Poof will still hit Slark in Shadow Dance.
* Dark Pact can only remove one Earthbind.
* 
Ransack will still affect Slark, even if he has a 
Black King Bar.
Legion Commander
* When Legion Commander uses Duel on one Meepo, he can use his other Meepos to kill her. If he wasn't dueled, he can help the teammate who was duelled to give the teammate the damage instead of Legion Commander.
* However, if Legion Commander picked up an Aghanim's Scepter and she duels one Meepo, that might be the end of Meepo if Legion managed to gather enough damage from previous duels.
Slark
* Heroes with AoE abilities will hit Slark in Shadow Dance: 
Lina, 
Jakiro, 
Underlord, 
Leshrac, 
Dark Seer, 
Earthshaker, 
Timbersaw, 
Crystal Maiden.
Legion Commander
* 
Atrophy Aura's percentage-based damage reduction greatly diminishes Legion Commander's overall damage output, even if she has won many Duels
* Legion Commander cannot get out the way of Firestorm because she is stationary.
Additional:
* Atrophy Aura makes it hard for Legion Commander to win Duels.
* 
Fiend's Gate can be used to save Underlord and his allies from a Duel or to intercept Legion Commander, because outside from 
Overwhelming Odds, Legion Commander has no other area-of-effect abilities.
Slark
* 
Slardar's level 25 talent makes 
Corrosive Haze undispellable, thus providing his allies vision of Slark.
Legion Commander
* With armor items like 
Solar Crest or 
Assault Cuirass combined with Bash of the Deep, Slardar can easily tank the Duel, If not dueled himself, he can drop 
Legion Commander's armor during duel and/or buff his teammate and save them, leaving her only the choice of dueling supports which can also be saved with fast Blink into Slithereen Crush.
Slark
* Heroes that can deny Slark early kills will prevent him from snowballing: Dazzle, Abaddon.
Legion Commander
* 
Shallow Grave prevents Legion Commander from killing her opponents in Duels.
* 
Shadow Wave will heal an ally caught in a Duel, as well as dealing damage to Legion Commander.
Slark
* Heroes who cannot prevent Sven from killing supports will always be at a disadvantage in fights such as Lina, Slark and 
Zeus.
Legion Commander
* 
God's Strength makes Sven one of the worst heroes to Duel.
* 
Storm Hammer can be used to interrupt Duels.
* 
Warcry gives a big boost in passive defensive ability with the active component to nearby allies.
* With the Aghanim Shard Warcry also gives nearby allies passive increases.
Slark
* Bulwark blocks much of Slark's basic attack damage, even during 
Shadow Dance.
* Slark finds it very difficult to have a good early/mid game when pressured in the early game by Spear of Mars and God's Rebuke.
* Spear of Mars and God's Rebuke can hit Slark through Shadow Dance and 
Depth Shroud.
* Should 
Pounce be on cooldown, Slark is very vulnerable inside Arena of Blood.
Legion Commander
* Because Duel requires both combatants to face each other, 
Bulwark's effectiveness will be increased by a huge margin, which makes it much more difficult for Legion Commander to win any duels against him.
* 
Spear of Mars and 
God's Rebuke pushes Legion Commander away during Duels against allies.
Additional:
* Bulwark immensely mitigates Duel, even with bonus physical damage, as Bulwark scales by percentage. Mars can also buy time for a dueled ally by pushing Legion Commander away with Spear of Mars.
Legion Commander
* Legion Commander is both good and bad vs Mars, on the plus side she can dispel Spear of Mars with 
Press the Attack and is a good 
Silver Edge carrier. However, Mars is not an ideal Duel target, as Bulwark will force her to 1: Buy Silver Edge, and 2: Hit Mars with it before the Duel, allowing a skilled Mars to react, especially with 
Eul's Scepter of Divinity. In teamfights, Mars will happily draw attention after using his abilities, and tank the Duel with all spells on cooldown.
Slark
* Heroes like Slark, 
Witch Doctor and others also tend to suffer in Ice Blast's heal denial.
Additional:
* 
Ice Blast stops Shadow Dance's passive health regeneration, even when Slark is not in vision.
Legion Commander
* Heroes with global abilities can give Legion Commander's opponent an edge in Duels from anywhere on the map: 
Nature's Prophet, 
Ancient Apparition, Zeus, 
Invoker, 
Treant Protector
Slark
* Heroes that lose a great amount of damage output and become less threatening: 
Phantom Assassin, 
Sven, Slark, 
Phantom Lancer.
* Once you have an Aghanim's Scepter, Shadow Demon instantly reaches a new power spike and becomes a counter for a variety of heroes that have strong passives.
* Heroes that lose a great amount of their tankiness and become easier to finish off: 
Bristleback, 
Spectre, Phantom Assassin, 
Enchantress, 
Dragon Knight.
* Heroes that lose a great amount of damage output and become less threatening: Phantom Assassin, Sven, Slark, Phantom Lancer.
* You can always stack camps and farm the scepter with Shadow Poison.
Legion Commander
* Heroes who can hide the Dueled target (
Outworld Destroyer, 
Shadow Demon, 
Tusk, 
Phoenix with Aghanim's Scepter etc).
Additional:
* Disruption can save allies and mess up an initiation from an enemy Legion Commander. Using Disruption on your ally that is affected by Duel will leave her totally exposed without the benefit of the life steal from 
Moment of Courage. A precise decision to Disrupt Legion Commander or her victim is crucial to waste Duel's potential.
* Demonic Purge cannot be dispelled by a hard dispel from Press the Attack, which in turn can be dispelled by your ultimate.
Slark
* Natural Order aura prevents Slark from gaining armor from the agility stolen with 
Essence Shift.
* Echo Stomp and Earth Splitter can hit Slark through his Shadow Dance ultimate.
* Slark's stats gain is relatively low compared to most agility carries making him quite squishy without his agility-based armor.
Legion Commander
* 
Gravekeeper's Cloak protects Visage from Legion Commander's attacks for most of Duel's duration.
* Chain stuns from Visage's familiars prevents Legion Commander from winning Duels.
Slark
* With Dark Ascension he can keep vision on Slark, disabling his Shadow Dance regeneration.
* Night Stalker is very fast so without the Pounce in lane, he can simply out distance him during the night.
* Slark is matched in night vision by only a few heroes, Night Stalker happens to be one of them.
Legion Commander
* Solar Guardian can save allies who are being dueled and will interrupt her Duel initiation.
Slark
* Bloodseeker is one of the hardest counters to Slark.Thirst prevents Slark from healing in lane with Shadow Dance and may set him up for a kill while in the jungle,or retreating.
* Rupture will deal damage during Pounce.
* 
Dark Pact cannot dispel Rupture, preventing Slark from escaping ganks.
Additional:
* 
Thirst stops Shadow Dance's passive health regeneration if Slark's current health is below the Thirst's visibility threshold.
* 
Rupture effectively diminishes Slark's mobility in battle, leaving him susceptible to AoE stuns or forcing to teleport out of the fight.
Slark
* Thunder Strike provides vision on him while Slark is invisible.
* Glimpse's range at lvl 3-4 is more than enough to pull him back to a favorable position for your team to group up and kill him.
* Even though he is capable of picking you off and deal enough damage to kill you, Slark will be literally sticking his neck out, since jumping on Disruptor means being on his battleground.
* AoE silence and the ability to mute Black King Bar is deadly to Slark at all stages of the game.
Additional:
* 
Static Storm and 
Kinetic Field locks down Slark, as he cannot use Dark Pact to dispel any disables, or Pounce out while silenced.
* 
Glimpse puts an end to any attempts at ganking Disruptor or his allies, and also negates Slark's mobility by bringing him back into the fight if he tries to escape with Pounce.
Slark
* Earthshaker's many stuns can lock down slippery heroes like Slark in his Shadow Dance and 
Weaver in his 
Shukuchi.
Additional:
* Earthshaker's many AoE stuns help lock down Slark and will often waste the duration of Shadow Dance.
* As a frequent 
Force Staff buyer, he can later on escape or save teammates from Pounce.
Legion Commander
* Earthshaker's AoE stuns can save ally against Duel, forcing Legion Commander to spend Aghanim's Scepter or Black King Bar.
Slark
* Heroes with invisibility and high mobility can jump on and focus down Earthshaker before he has a chance to initiate: 
Clinkz, Slark, 
Storm Spirit
Legion Commander
* 
Mystic Flare can easily burst down Legion Commander while she is Dueling.
Slark
* 
Toss and 
Avalanche deals heavy damage to Slark in the early game, making Tiny a very dangerous target to gank.
* Tiny has 0 agility, which means Slark's Essence Shift permanent agility steal does not do much against him.
Legion Commander
* 
Paralyzing Cask can save ally from Legion Commander Duel's until she purchases Aghanim's Scepter.
* 
Voodoo Restoration can heal Witch Doctor allies from Duel's.
* 
Death Ward can help Witch Doctor allies from winning Duel's, if, he is not a target.
Slark
* Shadow Dance does not protect Slark from Shadow Fiend's AoE spells.
Slark
* 
Phantom's Embrace cannot be dispelled by Slark's Dark Pact, and will cause him to suffer damage if he doesn't kill Phantom fast enough.
* 
Soulbind also cannot be dispelled by Slark's Dark Pact, and will cause Slark to suffer from a single-targeted ability used on his ally that is also affected by it.
Slark
* Dark Pact, Shadow Dance and Depth Shroud will do nothing against Onslaught and Trample, as they are both ground area-of-effect spells.
* Primal Beast has a gigantic hitbox, which could be difficult for Slark to escape with Pounce should Primal Beast choose to block him. Pounce also does not completely prevent Primal Beast from trampling offensively, as he still has some room to move.
* Primal Beast has a huge health pool making it difficult to shed it with Essence Shift and may allow Primal Beast to build Uproar stacks against him very rapidly.
* If Primal Beast buys an Aghanim's Scepter he can also break Essence Shift from working on attacks which is a big part of Slark's damage output.
Slark
* Slark's low health and reliance on high built armor from Essence Shift makes him susceptible to Muerta's 
Pierce the Veil.
* Muerta cannot be attacked by Slark's physical attacks and Essence Shift during Pierce the Veil.
* Muerta's 
Dead Shot and 
The Calling can hit Slark even while hidden with Shadow Dance.
Slark
* 
Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: Phantom Assassin, 
Magnus, Slark, 
Riki, 
Faceless Void, Storm Spirit.
Legion Commander
* Song of the Siren lasts long enough to prevent a successful Duel (but only if Naga wasn't the target).
Legion Commander
* Heroes who rely on illusions will see them destroyed easily by Overwhelming Odds: Phantom Lancer, 
Chaos Knight, 
Terrorblade, 
Naga Siren
Slark
* Heroes with heavy magical nukes will take advantage of Slark's poor HP or force him to use Shadow Dance early: Lina, 
Lion, Zeus
Legion Commander
* Heroes with global abilities can give Legion Commander's opponent an edge in Duels from anywhere on the map: Nature's Prophet, Ancient Apparition, Zeus, Invoker, Treant Protector
Slark
* Zeus can deal a huge amount of damage, but he lacks defensive abilities, such as good mobility or resistance. Due to that, he doesn't like to be touched by any means. Heroes with higher damage output and good mobility will often get easily near Zeus and trade damage (eventually causing Zeus's downfall). Such Heroes include: 
Lycan, Slark, Storm Spirit, Spectre and others.
Slark
* Heroes with AoE abilities will hit Slark in Shadow Dance: Lina, Jakiro, Underlord, Leshrac, Dark Seer, Earthshaker, Timbersaw, Crystal Maiden.
Legion Commander
* Heroes with global abilities can give Legion Commander's opponent an edge in Duels from anywhere on the map: Nature's Prophet, Ancient Apparition, Zeus, Invoker, Treant Protector
Legion Commander
* 
Troll Warlord's melee bash and high attack speed can often help him and his allies win Duels against Legion Commander.
Slark
* Heroes with AoE abilities will hit Slark in Shadow Dance: Lina, Jakiro, Underlord, Leshrac, Dark Seer, Earthshaker, Timbersaw, Crystal Maiden.
Slark
* Heroes with silencing abilities can be particularly deadly when Slark is trying to escape: 
Silencer, 
Death Prophet, 
Puck, 
Doom.
Legion Commander
* 
Fate's Edict prevents Legion Commander from attacking for a few seconds, potentially saving Oracle's ally.
* 
Fortune's End dispels Press the Attack's healing and attack speed buff, as well as the movement speed bonus from Overwhelming Odds.
* 
False Promise protects allies and prevents Legion Commander from winning Duels and gaining bonus damage.
Additional:
* Provided that the enemy team does not have an 
Axe, Oracle can guarantee that his ally survives for the duration of the Duel with False Promise and has decent nuke potential to help ally to win a Duel. He can also disarm Legion Commander with Fate's Edict.
* Oracle can dispel enemy buffs like Overwhelming Odds and Press the Attack with Fortune's End.
Legion Commander
* Heroes with long disables, like Lion, 
Night Stalker, or Legion Commander, can prevent Oracle from using spells or items.
Legion Commander
* Battery Assault's mini-stuns can severely disrupt Legion Commander's attack animation when she enters a Duel, potentially saving Clockwerk (or his allies) and possibly even giving him an edge in securing a win himself.
* Power Cogs pushes Legion Commander away from Clockwerk's allies when she enters a Duel.
Slark
* Clockwerk lacks burst damage, and that makes him vulnerable to heroes who can recover themselves and turn the fight around to their advantage after Clockwerk finishes his initiation. Additionally, Clockwerk hates buying 
Dagon and 
Ethereal Blade, which are the only itmes that can help him deal with heroes who can recover themselves and turn the fight around to their advantage: Faceless Void, Terrorblade, 
Ursa, Weaver, 
Broodmother, Slark, Abaddon, 
Wraith King, 
Lifestealer.
Slark
* Berseker's Call catches Slark in Shadow Dance, wasting its duration and preventing him from escaping to regenerate.
* Unlike most disables, Dark Pact cannot dispel Berserker's Call and the output damage would be returned by 
Blade Mail.
Additional:
* 
Berserker's Call forces Slark to attack him, even during Shadow Dance.
* 
Counter Helix will hit Slark in Shadow Dance. It will also trigger frequently against Slark's high attack speed provided by Essence Shift stacks.
* 
Culling Blade finishes off Slark before he gets a chance to slip away and regenerate his health, preventing him from playing his typical hit-and-run style.
Legion Commander
* Long lockdown is a great way to deal with Axe to prevent Berserker's Call from being used, heroes such as Legion Commander, 
Beastmaster and 
Primal Beast are good examples of this.
Slark
* Slark will have a hard time killing Sand King because of the survivability he gets from Burrowstrike and Sand Storm.
* Shadow Dance, which usually allows Slark to survive fights, is ineffective against Sand King's AoE damage.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: 
Anti-Mage, 
Earth Spirit, Faceless Void, Magnus, 
Mirana, 
Monkey King, 
Morphling, 
Pangolier, Phantom Assassin, Phoenix, Puck, 
Queen of Pain, Riki, 
Sand King, 
Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* Invoker's spells will disable and destroy Legion Commander while she's locked in a Duel.
Legion Commander
* Heroes with long lockdowns: 
Shadow Shaman, Legion Commander.
Slark
* 
Illusory Orb and 
Phase Shift allows Puck to avoid most ganking attempts.
* 
Waning Rift and 
Dream Coil makes it very hard for Slark to escape bad situations.
* Puck's abilities used together also deals significant magical nuke damage, none of which are targeted and thus cannot be avoided by Shadow Dance.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Slark
* Dark Pact is minimally effective against Phantasm illusions, and Slark lacks area damage otherwise.
* Pounce can be counteracted by Reality Rift.
* Slark is naturally frail and dies quickly to Chaos Knight's burst damage before he can build Essence Shift stacks.
* Be aware, however, that Shadow Dance can make Slark hard to kill as he can't be targeted during its duration.
Additional:
* 
Phantasms have enough health to survive Dark Pact, and Slark has no other source of AoE damage to deal with them.
Legion Commander
* Heroes with strong area damage to destroy Phantasm illusions: Axe, 
Ember Spirit, Legion Commander, Phoenix
Slark
* Slark has no sustained AoE to fight off Phantom Lancer's illusions as they continually spawn.
* Spirit Lance can give vision of Slark by spawning an illusion, making it harder for him to juke and gain the passive bonus from Shadow Dance.
* 
Phantom Rush helps Phantom Lancer chase down Slark if he tries to escape with Pounce.
Additional:
* Slark has no sustained AoE damage to deal with a lot of Phantom Lancer's illusions.
* 
Doppelganger lets Phantom Lancer dodge Dark Pact and Pounce and partially wastes the duration of Shadow Dance.
* 
Spirit Lance can give vision of Slark via spawning an illusion, making it harder for him to juke and gain the passive bonus from Shadow Dance.
* Phantom Rush helps Phantom Lancer chase down Slark when he jumps away with Pounce.
Legion Commander
* Heroes who rely on illusions will see them destroyed easily by Overwhelming Odds: Phantom Lancer, Chaos Knight, Terrorblade, Naga Siren
Additional:
* Overwhelming Odds deals high damage to Phantom Lancer's illusions.
* Duel's long duration prevents Phantom Lancer from using Doppelganger.
Slark
* Time Dilation while Dark Pact and Pounce are on cooldown will make these abilities unusable for a long time, reducing his escape potential. However, Time Dilation is dispellable with Dark Pact so it needs to be timed well.
* Chronosphere will not reveal Slark during Shadow Dance but covers the whole duration of Shadow Dance making him unable to use it to attack or escape. Slark still receives the regeneration benefit from Shadow Dance.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Slark
* Pounce helps put Windranger in place, even when she uses 
Windrun to escape.
* Shadow Dance avoids Windranger's attacks from 
Focus Fire altogether, and he can regenerate his health and fight back after Windranger uses up all her abilities.
* The stun from 
Shackleshot and the slow from
Powershot can be both dispelled by Dark Pact, provided Slark casts it at the right moment.
Legion Commander
* Press The Attack can save her allies dispels the stun from Shackleshot.
* Duel can lock down Windranger before she can escape with Windrun.
* Legion Commander tends to go for Blade Mail, which returns the damage she takes from Focus Fire.
Slark
* Dark Pact can dispel Flaming Lasso if is used in anticipation, but a Blink initiation from fog can catch the Slark off guard.
* Slark can also take off any Sticky Napalm stacks with Dark Pact in lane.
Additional:
* Shadow Dance's passive can inform Slark when he's under enemy vision, meaning it'll be very hard to catch Slark off-guard with 
Flaming Lasso.
* Flaming Lasso is dispelled by Dark Pact. Its casting can be prevented with Shadow Dance or Depth Shroud (it requires 
Aghanim's Shard).
Legion Commander
* Press the Attack dispels Flaming Lasso.
* Batrider is unlikely to win a Duel in any stage of the game.
Slark
* Essence Shift allows Slark to hit Bristleback freely whether on the front or back, stealing attributes and make Bristleback much less tanky.
* Pounce can be used to disengage and recover lost HP with his ultimate passive, and can return to fight in a short period while Bristleback is already injured and got some of his attributes stolen.
* Dark Pact makes it near impossible to keep the 
Viscous Nasal Goo debuff on Slark.
* Although Dark Pact cannot dispel 
Quill Spray, meaning that Slark will still receive quill stack damage even if he used Shadow Dance before.
* Slark builds Silver Edge in almost every game, an item that greatly counters Bristleback.
Legion Commander
* Duel makes Bristleback fight Legion Commander face to face, forcing him to take full damage.
* Press the Attack dispels the slow from stacks of Viscous Nasal Goo.
Additional:
* When dueled, Bristleback will have to face Legion head on, not allowing his passive 
Bristleback to come into effect.
Slark
* Sniper hugely lacks mobility and escape abilities so that he is an easy target for ganks from Slark.
Legion Commander
* Sniper's low mobility and lack of defensive abilities make him an easy gank target for the entire game, especially if Blink Dagger is picked up.
Slark
* Dark Pact dispels Dismember if timed correctly.
* Pounce allows Slark to escape Pudge's Rot once Dismember is over, and allows him to dodge hooks.
* Shadow Dance hides Slark and grants him a high degree of mobility, which can make him a difficult target to hook and also protects him from Pudge's Dismember (including allies with an Aghanim's Shard).
Legion Commander
* Legion Commander can use Press the Attack on an ally to dispel Dismember. The bonus health regeneration also partially counters the damage of Rot
* Duel can be used on Pudge whilst Rot is active, disabling toggling which may result in a lethal health drain that leaves Legion Commander with a successful duel.
Slark
* A well-timed Dark Pact can dispel Frost Arrows and Gust, letting Slark engage and escape freely.
* Essence Shift is very detrimental for Drow Ranger as the loss of agility means that Marksmanship will also suffer from getting weakened.
* Shadow Dance lets Slark quickly close the gap and deal heavy damage without giving Drow Ranger a chance to retaliate.
* Pounce counteracts Frost Arrows's slow, and also allows Slark easily pin Drow Ranger down or flee from her.
* Depth Shroud from Aghanim's Shard will allow Slark to save both, himself and his allies and will also allow them to freely fight back against Drow Ranger without her noticing them.
Additional:
* Pounce and items like 
Shadow Blade makes it very difficult for Drow Ranger to keep her distance from Slark, thereby losing her 
Marksmanship bonus.
* 
Gust is rarely enough to keep Slark at bay, as Drow Ranger has no movement abilities and will simply be chased down afterwards.
* Drow Ranger's heavy dependence on agility also makes her significantly weaker after being drained by Essence Shift.
Legion Commander
* Drow Ranger's low mobility and lack of defensive abilities make her an easy gank target in the early to mid-game.
* A Dueling Drow Ranger will lose her precious Marksmanship, reduce her damage output significantly, and will more likely lose that Duel.
Slark
* Heroes that can easily bypass Chen's creeps to get to Chen: Riki, Tusk, Clinkz, 
Sniper, Slark, Phantom Assassin, 
Void Spirit, Storm Spirit, Ember Spirit, Earth Spirit, Spirit Breaker.
Legion Commander
* Chen's fragility and low mobility make him an enticing Duel target.
* Overwhelming Odds and Moment of Courage can take advantage of converted creeps's numbers.
* With enough damage from Duel stacks, Legion Commander can also often kill any of Chen's unfortunate allies before he can use Hand of God.
Additional:
* Chen's frailty and low mobility make him an enticing Duel target.
* Overwhelming Odds and Moment of Courage can take advantage of converted creeps' numbers.
* With enough damage from Duel stacks, Legion Commander can also often kill any of Chen's unfortunate allies before he can use 
Hand of God.
Slark
* Dark Pact can dispel Venomous Gale and Poison Sting.
* Shadow Dance allows Slark heightened regeneration when out of vision making DoTs effects less threatening.
Legion Commander
* Heroes rely on their debuff to control the opponent will have a hard time against Press the Attack: 
Venomancer, Earth Spirit, 
Ogre Magi
Additional:
* Press the Attack dispels Venomous Gale and Poison Sting from Legion Commander or her teammates.
* Venomancer is an ideal target for Duel due to his lack of mobility and low starting health.
Slark
* 
Upheaval does not interrupt Slark too much, as he can just Pounce out of the area.
* 
Fatal Bonds and 
Shadow Word can be dispelled by Dark Pact.
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: Lycan, 
Arc Warden, 
Warlock, 
Chen
Slark
* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, 
Dawnbreaker, 
Enigma, 
Huskar, Jakiro, Legion Commander, Lina, 
Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.
Legion Commander
* Duel's long duration prevents Nyx Assassin escaping from 
Vendetta. With Aghanim's Scepter, she can also bypass 
Spiked Carapace.
Slark
* Pounce's root prevents Earth Spirit from using Rolling Boulder to escape, making it easier for Slark to shut him down especially in the laning phase.
Legion Commander
* Heroes rely on their debuff to control the opponent will have a hard time against Press the Attack: Venomancer, Earth Spirit, Ogre Magi
Slark
* Dark Pact dispels Ignite's slow and Fireblast's stun.
* Shadow Dance allows Slark to regenerate HP, even when he is affected by Ignite and Fireblast.
Legion Commander
* Heroes rely on their debuff to control the opponent will have a hard time against Press the Attack: Venomancer, Earth Spirit, Ogre Magi
Slark
* Heroes with escaping and disjointing abilities can be good against Juggernaut:Anti-Mage Riki, Queen of Pain, Puck, Storm Spirit, Ember Spirit, Slark etc.
Additional:
* 
Blade Fury does not offer any protections against Essence Shift, as it can go through spell immunity and reduces attribute.
* Slark can pounce away from Juggernaut and he cannot prevent or chase slark.
* Shadow Dance prevent Juggernaut from using 
Omnislash altogether, while regen himself at a higher rate. Slark can freely hit juggernaut without any fears of retaliation.
Legion Commander
* Duel pierces spell immunity and forces him to attack Legion Commander, making him unable to use Omnislash.
Slark
* Heroes who build mana boosting items but have low mana regeneration are especially vulnerable against Mana Break and Mana Void: Timbersaw, Slark, 
Shadow Fiend, Clinkz, Bristleback 
Nyx Assassin, Magnus
Slark
* Pounce prevents Anti-Mage from using Blink, and lets him disengage from Anti-Mage if needed.
* Essence Shift allows Slark to permanently steal agility from Anti-Mage.
* Shadow Dance stops Anti-Mage from being able to fight back in a slippery situation.
Legion Commander
* Duel renders Anti-Mage's escape capabilities with Blink and Counterspell useless. Blade Mail and Moment of Courage work well against Anti-Mage's relatively low health.
* A good initiation from Legion Commander and her team is enough to effortlessly kill Anti-Mage.
Additional:
* 
Counterspell offer no protection against Duel at all.
* Duel locks down Anti-Mage for a long duration, preventing him from escaping with 
Blink. One successful Duel initiation is usually enough for Legion Commander's team to kill Anti-Mage.
Legion Commander
* Heroes with abilities that blind or cause Legion Commander to miss will prevent her from winning Duels: Arc Warden, 
Keeper of the Light, Riki, 
Tinker
Slark
* Pounce prevents Tinker from blinking away.
* Slark frequently builds Shadow Blade, which allows him to approach Tinker unnoticed. Since Tinker's farming usually covers a significant amount of area on the map, Sentry Wards may not be cost effective.
* Shadow Dance allows Slark to detect both common and unusual wards. Eliminating common ward causes Tinker trouble farming many lanes if he does not know who may be waiting to jump on him. Slark is also uniquely able to identify some of the less common wards used by Tinker, such as those placed on the cliffs at map edges which Tinker uses to give him vision over the trees he uses to hide in.
* Slark's extremely high move speed from Shadow Dance, potentially stacked with Shadow Blade, allows him to easily follow Tinker between lanes, especially if Tinker has pushed the lanes out.
* Dark Pact dispels Laser's blind.
Legion Commander
* Press the Attack can dispel Laser's blind while providing great attack speed and health regeneration.
* Once caught in a Duel, Tinker, who completely relies on his spells to be effective, has little chances of survival with his low health pool and armor.
Slark
* Lycan cannot escape from a Pounce even if he uses 
Shapeshift, and has no disabling abilities to stop Slark.
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: Lycan, Arc Warden, Warlock, Chen
Slark
* Slark with Dark Pact
* Heroes that can remove the Track debuff with their skills:
* Abaddon with Aphotic Shield and Borrowed Time
* Huskar with 
Life Break
* 
Juggernaut with Blade Fury
* Legion Commander with Press the Attack
* Lifestealer with 
Rage and 
Infest
* Naga Siren with 
Mirror Image
* 
Omniknight with 
Heavenly Grace
* 
Oracle with Fortune's End and False Promise
* Phantom Lancer with Doppelganger
* Slark with Dark Pact
* Ursa with 
Enrage
* Weaver with 
Time Lapse
* 
Tidehunter with 
Kraken Shell when damage received reaches the threshold.
Legion Commander
* Legion Commander with Press the Attack
* Heroes that can remove the Track debuff with their skills:
* Abaddon with Aphotic Shield and Borrowed Time
* Huskar with Life Break
* Juggernaut with Blade Fury
* Legion Commander with Press the Attack
* Lifestealer with Rage and Infest
* Naga Siren with Mirror Image
* Omniknight with Heavenly Grace
* Oracle with Fortune's End and False Promise
* Phantom Lancer with Doppelganger
* Slark with Dark Pact
* Ursa with Enrage
* Weaver with Time Lapse
* Tidehunter with Kraken Shell when damage received reaches the threshold.
Legion Commander
* Heroes that cannot move in fights such as a Dueling Legion Commander or anyone channeling a spell like 
Bane, 
Pudge, or Enigma are easy Sacred Arrow targets.
Slark
* If Slark sees the Sacred Arrow before it hits him, he can use Dark Pact to remove it a moment later.
* Pounce prevents Mirana from escaping with Leap.
* Slark can survive Mirana's Aghanim's Scepter​ combo with Shadow Dance.
Legion Commander
* Heroes that can protect or dispel stunned allies such as Legion Commander, Outworld Destroyer, Shadow Demon and Oracle can reduce the effectiveness of Sacred Arrow.
Slark
* Slark's Pounce can be used to dodge Hoodwink's abilities or lock her down.
* Shadow Dance makes Slark unhittable from 
Acorn Shot.
* Dark Pact removes all slows from Hoodwink's abilities.
* Hoodwink's already low health output is a great target for Slark's Essence Shift.
Slark
* Dark Pact rips through 
Refraction charges and still steals attributes during Refraction.
* Pounce and Dark Pact will still hit Templar Assassin while she is 
Melded. Since she cannot move, both abilities will be easy for Slark to land.
Slark
* Rubick usually positions in the back of a team. Heroes who can sneak up and assault Rubick (e.g. Slark) or damage Rubick from great distance (e.g. Spectre, Sniper) should be treated cautiously, as otherwise the matchup usually ends up badly for Rubick.
Slark
* Pounce and Dark Pact together with some attacks can take Rubick down quickly.
* Rubick's spells are ineffective due to the strong dispel effect of Dark Pact.
* Even though Shadow Dance is a great spell to steal, Slark's untargetable nature and his low cooldown spells prevents Rubick from stealing. Also Slark can freely use other abilities for the duration of Shadow Dance.
Legion Commander
* Heroes with low health will die easily during Duels, and can be farmed for damage in the early game: Crystal Maiden, 
Lich, 
Techies, 
Rubick
Legion Commander
* Duel's long duration prevents Weaver from activating Time Lapse or escaping with Shukuchi.
Legion Commander
* Duel's long duration prevents Terrorblade from swapping his health with 
Sunder.
* Overwhelming Odds deals high damage to Terrorblade's illusions.
Legion Commander
* Heroes with abilities that blind or cause Legion Commander to miss will prevent her from winning Duels: Arc Warden, Keeper of the Light, Riki, Tinker
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* Another great threat to Riki since her Duel forces him to fight from the front and expose him for the entire duration, almost always guaranteeing an easy win (unless Riki has allies helping him).
* Moment of Courage can become hard to deal with as it doesn't cease with silence.
Legion Commander
* 
Searing Arrows and Clinkz physical damage items are almost suicidal when used on Legion Commander, as it invites an instant Duel and Legion Commander herself is a natural Blade Mail carrier.
* Duel locks down Clinkz for a long duration, preventing him from escaping with 
Skeleton Walk.
Slark
* Slark's Pounce allows him to close the gap on Phantom Assassin and prevent her from escaping with 
Phantom Strike.
* As a hero who typically builds Silver Edge, Slark can use it to disable Phantom Assassin's 
Blur and 
Coup de Grace, thus taking down her attack evasion and drastically reducing her damage output.
* Because Phantom Assassin is always reliant on critical strikes, Slark will have plenty of time to escape with Pounce, Shadow Dance and Silver Edge (provided that he purchased it already).
* Depth Shroud from Aghanim's Shard will allow Slark to save both, himself and his allies from Phantom Assassin with Shadow Dance, and to freely fightback against her without removing invisibility upon attacking.
* Essence Shift is much more harmful for Phantom Assassin than for other heroes, as losing the agility means that her physical damage will be also reduced, which can also weaken Coup de Grace if Slark manages to steal lots of agility from her.
* Overall, any attempt for Phantom Assassin to take down Slark will hurt her more than Slark.
Additional:
* Slark's Pounce allows him to close the gap on Phantom Assassin and prevent her from escaping with Phantom Strike.
* As a hero who typically builds Silver Edge, Slark can use it to disable Phantom Assassin's Blur and Coup de Grace, thus taking down her attack evasion and drastically reducing her damage output.
* Because Phantom Assassin is always reliant on critical strikes, Slark will have plenty of time to escape with Pounce, Shadow Dance and Silver Edge (provided that he purchased it already).
* Depth Shroud from Aghanim's Shard will allow Slark to save both, himself and his allies from Phantom Assassin with Shadow Dance, and to freely fightback against her without removing invisibility upon attacking.
* Essence Shift is much more harmful for Phantom Assassin than for other heroes, as losing the agility means that her physical damage will be also reduced, which can also weaken Coup de Grace if Slark manages to steal lots of agility from her.
* Overall, any attempt for Phantom Assassin to take down Slark will hurt her more than Slark.
Slark
* Shadow Dance allows Slark to not be targeted by Unstable Concoction, making Alchemist stun himself and making himself vulnerable to the enemy.
* Dark Pact also allows him to just purge off the stun if timed correctly.
* Essence Shift will steal stats over long durations at a time should Alchemist lack the damage to kill Slark.
Slark
* Essence Shift deals 20 extra damage by draining one strength per hit, which cannot be reduced or spread by 
Dispersion.
* Pounce prevents Spectre from escaping with 
Spectral Dagger.
* 
Haunt illusions usually don't deal a lot of damage to Slark as he tends to buy a Shadow Blade, preventing 
Desolate's and 
Diffusal Blade's damage and activating Shadow Dance's regeneration to make up for any damage caused by 
Radiance.
* Slark is a natural carrier of Silver Edge, which helps break both Desolate and Dispersion.
Slark
* Dark Pact dispels debuffs from Gush, Anchor Smash and even Ravage if timed correctly.
* Kraken Shell cannot restore attributes stolen by Essence Shift or dispel the leash if he gets Pounced.
Slark
* Heroes with silencing abilities can be particularly deadly when Slark is trying to escape: Silencer, Death Prophet, Puck, Doom.
Slark
* Slark's Dark Pact allows him to dispel Silencer's debuffs.
* Against a carry Silencer, Essence Shift will lower damage from both Glaives of Wisdom and his basic attack.
Legion Commander
* Heroes that can disable or silence Silencer for a long time, such as Bane and Legion Commander, can lock down Silencer while their allies put him down.
Legion Commander
* Overwhelming Odds's damage stacks with each enemy unit in its radius. If this hits Broodmother and a large number of spiders it can deal significant amounts of damage.
* Moment of Courage has a high chance to proc if Broodmother and all of her spiders are attacking her.
* Duel can keep Broodmother in place long enough for Legion's team to kill her.
Additional:
* Overwhelming Odds is great at killing many stacked up spiderlings, thus giving Legion Commander a large buff.
* Duel is a reliable way to lock down Broodmother, preventing her from running into the treeline.
Slark
* Shadow Dance allows Slark to attack Lifestealer for its duration without any way for Lifestealer to fight back, allowing him to steal his stats with Essence Shift, which also reduces Lifestealer's strength and, therefore, health pool.
* Slark can easily escape Lifestealer with Pounce, and can avoid Open Wounds with Dark Pact should Lifestealer be forced to itemize for it.
* Slark commonly buys a Silver Edge, which can break Lifestealer's Feast, severely diminishing his damage output and lifesteal.
* Depth Shroud from Aghanim's Shard allows Slark to save both, himself and his allies with Shadow Dance while also allowing them to fight back against Lifestealer.
Slark
* Heroes that can jump on her: Slark, Queen of Pain, Anti-Mage
Legion Commander
* Heroes with low health will die easily during Duels, and can be farmed for damage in the early game: Crystal Maiden, Lich, Techies, Rubick
Legion Commander
* Heroes with global abilities can give Legion Commander's opponent an edge in Duels from anywhere on the map: Nature's Prophet, Ancient Apparition, Zeus, Invoker, Treant Protector
Slark
* Pounce also stops Nature's Prophet's 
Teleportation.
Legion Commander
* Legion Commander's Overwhelming Odds deals damage for every Treant it hits, which allows it to easily wipe out large waves of them.
Slark
* Heroes with strong dispels can remove Primal Roar's stun: Abaddon, Slark, Oracle.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Slark
* Both Scream of Pain and Sonic Wave should hit Slark during his Shadow Dance.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* Duels prevents Queen of Pain from using Blink, which may force her to purchase a 
Linken's Sphere
* Because Queen of Pain is also not a right-click hero, Legion won't have much difficulties in duels.
* Press the Attack dispels Shadow Strike's debuff.
Legion Commander
* Carries that can out damage Huskar will do well against him: Legion Commander, Faceless Void, Troll Warlord, Phantom Assassin.
Additional:
* Life Break is almost suicidal when used on Legion Commander, as it invites an instant Duel and Legion Commander herself is a natural Blade Mail carrier.
* Huskar's low survivability and mostly on low health make him particularly vulnerable to Legion Commander's high physical damage.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* 
Tethered heroes are much harder for Legion Commander to kill in Duels.
* 
Relocate can cancel Duels and save allies.
Slark
* Heroes that can easily bypass Io's allies to get to Io: Riki, Tusk, Clinkz, Sniper, Slark, Phantom Assassin, Void Spirit, Storm Spirit, Ember Spirit, Earth Spirit, Spirit Breaker, Lifestealer.
Legion Commander
* Duel is very effective against Io due to its low health and armor.
Slark
* Heroes who have a high mobility (Queen of Pain, Storm Spirit, Slark, etc.).
Legion Commander
* Special mention to Legion Commander, as she can lock down Void Spirit for a long amount of time without worrying too much about being killed by him during the Duel.
Legion Commander
* Heroes with long or multiple disables will prevent Legion Commander from winning Duels: Shadow Shaman, Lion
Slark
* Nyx Assassin, 
Bounty Hunter and Slark can all sneak up and kill Shadow Shaman, Nyx being particularly deadly. Shadow Shaman must watch out for Slark carefully, as he can break either (but not both unless he makes a mistake) of Shadow Shaman's disables, with Dark Pact and leap out of a serpent ward ring. These heroes, however, rely heavily on escape and are themselves not very durable and none of them can survive a full lockdown with Mass Serpent Ward. Having Sentry Wards can turn Shadow Shaman from prey to predator.
Legion Commander
* Pudge, Legion Commander and Axe will make the match a living hell for Shadow Shaman, since they are known for surprise attacks from the fog and quickly killing low HP heroes. They can also interrupt Shadow Shaman's channeling, Legion being especially problematic, as she can use Press the Attack on an ally who is hexed as well.
Legion Commander
* Heroes with low health will die easily during Duels, and can be farmed for damage in the early game: Crystal Maiden, Lich, Techies, Rubick
Slark
* Heroes with heavy magical nukes will take advantage of Slark's poor HP or force him to use Shadow Dance early: Lina, Lion, Zeus
Legion Commander
* Heroes with long or multiple disables will prevent Legion Commander from winning Duels: Shadow Shaman, Lion
Slark
* Lion's lack of escapes gives Slark easier time to catch him through Pounce.
* Shadow Dance gives Slark the advantage of being untargetable, nullifying single target abilities (such as non-upgraded 
Hex, 
Mana Drain and 
Finger of Death).
* Dark Pact applies multiple instances of strong dispel on Slark, which is strong against any of Lion's disables.
* Lion's low health pool and low armor make him extremely vulnerable to Slark's damage output.
Legion Commander
* Lion is extremely dependent on his abilities. Silences like Silencer's 
Last Word, magic resistance like Oracle's Fate's Edict, and dispels like Legion Commander's Press the Attack all make his abilities less effective.
Slark
* Heroes that rely on their high mobility such as Queen of Pain, Slark and Weaver can be constantly engaged against due to your excellent ability to chase over any terrain. Make sure you carry true sight items (such as 
Dust of Appearance or 
Gem of True Sight) for invisible heroes that could potentially escape your clutches.
Slark
* Pounce's leash prevents Storm Spirit from using 
Ball Lightning, making it hard for Storm Spirit to escape a gank from Slark.
* Dark Pact can dispel 
Orchid Malevolence's Soul Burn.
Slark
* Heroes with silencing abilities can be particularly deadly when Slark is trying to escape: Silencer, Death Prophet, Puck, Doom.
Legion Commander
* Duel is a great initiation to kill Death Prophet before she can cast Exorcism. Furthermore, Legion Commander often builds Blade Mail and can reflect Exorcism's damage to kill Death Prophet easily.
Slark
* Heroes with heavy magical nukes will take advantage of Slark's poor HP or force him to use Shadow Dance early: Lina, Lion, Zeus
Slark
* Dark Pact can be cast during the cast animation of Light Strike Array and dispel its stun.
* Pounce allows Slark to close the gap to Lina.
* Shadow Dance prevents Lina from killing Slark with her Laguna Blade when his HP gets low.
Slark
* Heroes with Break abilities will prevent Slark from regenerating and gaining Essence Shift stacks: 
Viper, Shadow Demon, etc.
Additional:
* 
Viper Strike can disable Essence Shift and the regeneration aspect of Shadow Dance.
* Dark Pact doesn't mean a lot against Viper's ubiquitous slows.
* Viper becomes a relevant presence in team fights before Slark can procure his standard items (e.g. Shadow Blade).
Legion Commander
* Viper's frailty and low mobility make him an enticing Duel target and 
Corrosive Skin doesn't protect him against Legion Commander physical attacks.
* Press the Attack can dispel 
Poison Attack.
* Viper slows can easily negate by Overwhelming Odds movement speed.
Slark
* Melee carries during the laning phase: Sven, Slark
Legion Commander
* Heroes with abilities that blind or cause Legion Commander to miss will prevent her from winning Duels: Arc Warden, Keeper of the Light, Riki, Tinker
Slark
* Heroes with dispels: Legion Commander, Oracle, Slark, Phantom Lancer
Legion Commander
* Press the Attack can dispel Blinding Light or Solar Bind from a hero.
* Duel can be used to instantly take Keeper of the Light out of a team-fight.
Legion Commander
* Wraith King's 
Reincarnation allows him to severely punish Legion Commander after he revives, as her abilities are on cooldown. Legion Commander is still awarded a Duel win if Wraith King reincarnates.
Additional:
* Wraith King makes a poor Duel target, as he can be already quite hard to bring down once, and then you have to worry about his second life.
* However, even if Legion Commander does win the duel when Reincarnation is off cooldown, she still receives the permanent victory damage bonus because taking down Wraith King's first life still counts as a "kill".
Slark
* Dark Pact, if timed correctly, can dispel Wraithfire Blast's stun and slow.
* Since Wraith King has a lot of health and multiple lives, Slark can keep gaining Essence Shift stacks, increasing armor, damage, and attack speed and can beat down Wraith King twice.
* Slark sometimes carries Diffusal Blade to burn mana as an attempt to shut down Reincarnation.
* Because Wraith King has no AoE abilities, Shadow Dance is particularly useful against Wraith King.
Legion Commander
* Magnetic Field prevents Legion Commander from getting wins with Duel.
Additional:
* 
Magnetic Field prevents Legion Commander from easily gaining wins with Duel.
Slark
* Melee carries who usually buy an early Black King Bar, and have gap closing abilities can be good against the Arc Warden, such as Slark, Riki, Earthshaker with Aghanim's Scepter, Sven with Aghanim's Scepter etc.
Additional:
* 
Flux is dispelled by Dark Pact.
* Pounce allows Slark to avoid 
Spark Wraiths.
* 
Tempest Double allows Slark to build up Essence Shift stacks, especially when it is being used for split pushing.
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: Lycan, Arc Warden, Warlock, Chen
Legion Commander
* Heroes that lack burst damage will have a difficult time taking down Monkey King, and fare badly against Jingu Mastery: Legion Commander, Lifestealer, Weaver, Wraith King
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* Heroes who can hide the Dueled target (Outworld Destroyer, Shadow Demon, Tusk, Phoenix with Aghanim's Scepter etc).
Additional:
* Walrus PUNCH! makes Legion Commander lose Duel easily, especially when she doesn't have Blade Mail. Tusk can also snowball dueled allies, preventing them from taking damage for a large portion of the duel's duration.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Slark
* Heroes with AoE abilities will hit Slark in Shadow Dance: Lina, Jakiro, Underlord, Leshrac, Dark Seer, Earthshaker, Timbersaw, Crystal Maiden.
Additional:
* Timbersaw can use 
Chakram as a scouting tool to find Slark if he tries to Pounce into the trees.
* None of Timbersaw's abilities require a target to be cast, allowing him to hit Slark inside Shadow Dance.
* 
Reactive Armor can be effective protection against a Slark who attacks quickly, since the strong armor and health regen cannot be stolen by Essence Shift.
* 
Timber Chain makes Timbersaw very mobile, meaning he is among the very few heroes who can actually give chase to a fleeing Slark.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* 
Static Link drains Legion Commander's accumulated damage, effectively neutralizing her overall primary advantage, and prevents her from winning Duels.
* 
Storm Surge's movement speed buff makes Razor and his allies harder to catch and initiate.
* 
Eye of the Storm, if used beforehand, will always hit Legion Commander during Duels, due to her forced proximity. This drastically lowers her survivability during Duel.
Slark
* Pounce can easily break Static Link, making it less powerful against him.
* Slark is one of the few heroes who can man fight a Razor, because of Essence Shift.
* Shadow Dance can prevent Razor from killing him and may provide an opportunity to kill Razor due to it preventing Razor from attacking Slark.
Legion Commander
* 
Lucky Shot can disarm Legion Commander and reduce her armor, which can reduce her chances of winning a duel. If an ally is targeted, Pangolier can simply use 
Swashbuckle to inflict it on her.
* If an enemy Pangolier casts a well-timed 
Rolling Thunder before Legion Commander can cast Duel, it might result in her chasing down Pangolier until his or her ultimate ends, whichever duration ends first, resulting in an open window for enemy allies to target Legion Commander, making her vulnerable and susceptible to any source of attacks. If Legion Commander has an Aghanim's Scepter in her inventory, the risk of wasting a solid 8 seconds would result in a futile duel.
* Dueling Pangolier is normally a mistake, Pangolier can disarm you in the duel, and potentially gain some Duel damage, Only duel Pangolier if at least 1 ally is nearby, and he is on low health, And even then, be wary, A good duel can easily turn against you with one Lucky Shot (Due to Lucky Shot lasting 4 seconds).
Additional:
* Swashbuckle can be used to disarm Legion Commander while she is Dueling an ally, granting her opponent a considerable advantage, Lucky Shot lasts 4 seconds at most wasting Legion Commander's entire Duel, (Or half, if Legion Commander has the Scepter).
* Legion Commander will try not to duel Pangolier alone, as she will almost inevitably lose, thanks to Lucky Shot's disarm, If Legion Commander wants to duel a Pangolier, she must be with atleast a teammate, and if she has her scepter, 3 or 4 teammates.
* Legion Commander is often with her allies, allowing you to rack up some considerable damage resistance with Shield Crash.
Slark
* Dark Pact easily purges away both slow and disarm effect from Lucky Shot.
* With Pounce now applying leash to the target, Pangolier is helpless against Slark since both his Swashbuckle and Rolling Thunder will be disabled. Pounce also help Slark to easily escape from Rolling Thunder.
Slark
* With Dust of Appearance, Luna will be able to use 
Eclipse on invisible heroes. Be mindful that Slark is exception because he'll be able to remove the debuff with Dark Pact.
Legion Commander
* A well-timed Eclipse before a Duel usually prevents Legion Commander from winning Duels, if Luna is the target.
* Meanwhile, when Luna is not a target, Eclipse and 
Lucent Beam can also help an ally win a Duel against Legion Commander.
* However, skilled Legion Commander will always buy a Black King Bar to block Eclipse and Lucent Beam or Aghanim's Scepter to reduce it's damage.
Additional:
* A well-timed Eclipse before a Duel usually prevents Legion Commander from winning Duels if Luna is the target. Luna can also buy Linken's Sphere to block Duel.
* Meanwhile, when Luna is not a target, Eclipse and Lucent Beam can also help an ally win a Duel against Legion Commander.
* Bear in mind, however, that skilled Legion Commander will always buy a Black King Bar to block Eclipse and Lucent Beam or Aghanim's Scepter to reduce their damage.
Slark
* Shadow Dance prevents Luna from damaging Slark, and together with Silver Edge he can easily chase her or escape from her.
* Luna has no way to escape from Pounce's leash, which is especially bad as she is not used to buying 
Wind Waker, which is the only way to escape from Pounce outside of Black King Bar.
* For the same reasons, Slark makes a very powerful ally for Luna when they are in the same team.
Additional:
* Luna's lack of mobility and escape abilities makes her easily to gank for Slark.
* Shadow Dance helps avoid all the damage from Eclipse.
* For the same reasons, Slark makes a very powerful ally for Luna when they are in the same team.
Legion Commander
* Heroes that can keep Luna locked down for a long time can be a threat (she is very item and spell dependent): Faceless Void, Legion Commander, Doom.
Slark
* Though Slark's large damage output is most certainly a concern for the squishy Crystal Maiden, she does perform fairly well against him when coupled with aid from her team.
* Slark has no innate way to cancel Freezing Field, but the common purchase of 
Skull Basher does make Slark a substantially greater threat to Crystal Maiden as the game progresses.
* Freezing Field can still hit Slark while he is under the effect of Shadow Dance, and for the early and mid game, the damage output of Crystal Maiden's ultimate outscales Slark's passive regeneration, making a quick use of Freezing Field as soon as Slark uses Shadow Dance a great way to combat him.
* Crystal Maiden's Frostbite and Crystal Nova are helpful in disabling and slowing the slippery Slark so he can be killed by her teammates.
Legion Commander
* Duel is a great initiation to target Crystal Maiden with, as it prevents her from using Freezing Field or any other abilities and allowing the enemy team to quickly kill her before she can aid her team in a fight.
Slark
* Heroes with AoE abilities will hit Slark in Shadow Dance: Lina, Jakiro, Underlord, Leshrac, Dark Seer, Earthshaker, Timbersaw, Crystal Maiden.
Slark
* Dark Seer relies on Surge for most of his mobility, so he's not very vulnerable to slows, but much more to root effects and walls or pseudo-walls such as 
Disruptor's Kinetic Field or Slark's Pounce.
Legion Commander
* 
Fury Swipes can give Ursa the edge in Duels.
* Enrage's instant cast time allows it to be used before Legion Commander initiates a Duel, causing Ursa to take almost no damage for a brief period of time.
* However, Duel stops Ursa from casting Enrage at the most critical moment
Slark
* Slark can detect early Roshan attempts due to Shadow Dance if he frequently checks the Pit.
* Enrage cannot restore attributes stolen by Essence Shift and will reduce his physical damage output.
* Even if Ursa initiates with Earthshock, Slark can Pounce away or use Dark Pact after Ursa's initiation to avoid Fury Swipes' damage until Earthshock's slow is gone.
Legion Commander
* Heroes who can hide the Dueled target (Outworld Destroyer, Shadow Demon, Tusk, Phoenix with Aghanim's Scepter etc).
Additional:
* Legion Commander relies on her powerful attack and her Duel to be effective. But if Phoenix gets the jump on her first, she can find herself severely slowed, taking heavy damage, and find herself unable to Duel a burning Supernova.
* It must be noted that Press the Attack will both dispel the attack slow of Fire Spirits and grant her or whoever she targets bonus attack speed. This allows her to easily destroy a Supernova if caution is not taken to prevent this from occurring. As such, it would be a better decision to simply avoid a farmed or skilled Legion Commander instead of attempting to overpower her.
* If an ally is caught by Duel, Phoenix can use Sun Ray to heal the ally and damage Legion Commander, possibly swinging the Duel in their team's favor. Or with Aghanim's Scepter, Phoenix can save an ally from dying in Duel with Supernova and cancel the Duel as well.
Slark
* Heroes with blink or movement abilities, which are disabled by Pounce's leash: Anti-Mage, Earth Spirit, Faceless Void, Magnus, Mirana, Monkey King, Morphling, Pangolier, Phantom Assassin, Phoenix, Puck, Queen of Pain, Riki, Sand King, Spirit Breaker, Timbersaw, Tusk.
Legion Commander
* Enigma can be a perfect counter-initiator with his ultimate. A perfectly timed Black Hole will turn the tide of any initiation, especially from heroes like; Spirit Breaker, Legion Commander, Axe, Puck, and Slardar.
Slark
* Enigma lacks burst damage, and that makes him vulnerable to heroes who can recover themselves and turn the fight around to their advantage after Enigma finishes his initiation: Faceless Void, Terrorblade, Ursa, Weaver, Broodmother, Slark, Abaddon, Wraith King, Lifestealer.
Slark
* Low-health, normally mobile carries who rely entirely on raw attack damage are vulnerable to Bane's nukes and disables: Anti-Mage, Clinkz, 
Drow Ranger, Faceless Void, 
Gyrocopter, Juggernaut, 
Meepo, Mirana, Monkey King, Morphling, Phantom Assassin, Phantom Lancer, Riki, Shadow Fiend, Slark, Sniper, Terrorblade, Troll Warlord, Weaver.
Legion Commander
* Bane has powerful single-target abilities that can help his allies win Duels, or at least cripple Legion Commander for the duration.
* Nightmare can waste Duel's entire duration as the dueled units transfer the Nightmare back and forth. This may be prevented if a non-Dueling unit attacks the Nightmared Dueler.
Additional:
* 
Enfeeble, 
Nightmare and 
Fiend's Grip all prevent Legion Commander from winning Duels, especially when Bane has 
Blink Dagger.
Slark
* Dark Pact can dispel Enfeeble, as well as Nightmare and Fiend's Grip when timed correctly.
* Shadow Dance can protect Slark from Bane's single-target abilities.
Legion Commander
* Heroes with strong dispels can dispel Bane's disables from their allies: Oracle, Legion Commander, Omniknight.
Legion Commander
* 
Cold Embrace saves allies from dying in Duels.
* 
Winter's Curse turns Legion Commander's high damage against her allies, giving the enemy team little time to react.
* However, Winter Wyvern lanes very poorly against Legion Commander due to Press the Attack removing all the debuffs she can give. Winter Wyvern also has little chances of surviving if she gets Dueled herself.
Additional:
* Cold Embrace is very effective against Duel.
* Also, casting Winter's Curse at Legion Commander while an ally is in a Duel will stun her for most of the duration, possibly preventing lethal damage dealt to your ally. It can also turn her high-damage against her teammate.
Slark
* Arctic Burn and Splinter Blast's debuffs are can be dispelled with with Dark Pact. Arctic Burn also cannot be used to escape against Pounce.
* Even though Cold Embrace can protect it's owner from Slark's direct attacks, Slark can still gain Essence Shift stacks from attacking heroes affected by it.
* However, Essence Shift works against allies, and Slark's low health pool means that if he's the target for Winter's Curse, he will go down very quickly as Winter's Curse cannot be dispelled at all.
Legion Commander
* 
Mana Shield makes Medusa very hard to take down in Duels.
* 
Stone Gaze stops Legion Commander from Dueling altogether, regardless of who she targets.
Slark
* Medusa is especially vulnerable to Essence Shift, as both strength and intelligence contribute to her effective HP, while agility contributes to her damage.
* Dark Pact when timed right can be used to dispel Stone Gaze right after it petrifies Slark, allowing him to keep attacking Medusa throughout the duration.
Additional:
* Medusa cannot chase Slark in any way and has no disable beyond her ultimate, making her unable to stop him getting away and regenerating before coming back to finish her off.
* Essence Shift particularly removes 1 intelligence point per hit, thus lowering Medusa's mana pool's cap and leaving her much more vulnerable in prolonged fights.
Slark
* Outworld Destroyer can disrupt Slark's attacks with
Astral Imprisonment either by banishing Slark or his target.
Arcane Orb if he is directly attacked by Outworld Destroyer
Sanity's Eclipse if he tries to run with 
Shadow Dance
Arcane Orb deals pure damage, which ignores the armor granted from permanent agility stacks.
Astral Imprisonment can disrupt any Pounce attempt by banishing the leashed ally.
Sanity's Eclipse.
* Slark's low heathpool means he will die quickly to
* Slark has low intelligence gain, making him easy to finish with
Additional:
*
*
* Slark's low mana pool makes him more susceptible to
Legion Commander
*
Astral Imprisonment prevents Legion Commander from killing her opponents in Duels.
Duel with Astral Imprisonment, and he can inflict heavy damage on Legion Commander with Arcane Orb to aid his ally. However, if he gets caught, he is unlikely to survive the duel, due to his lack of durability.
Additional:
* Outworld Destroyer can save an ally hero caught by