Pugna
* Pugna's squishiness and lack of mobility make him easy prey for a Hookshot initiation.
* Clockwerk's high health, low mana costs, and lack of reliance on Blink Dagger make 
Nether Ward ineffective.
* Battery Assault shuts down 
Aghanim's Scepter upgraded 
Life Drain, as the repeated ministuns prevent Pugna from channeling for an extended length of time.
Additional:
* Clockwerk loves to 
Hookshot low health, immobile targets like Pugna.
* Pugna's Life Drain gets immediately and repeatedly (if an Aghanim's Scepter was purchased) cancelled due to 
Battery Assault, especially if Pugna is trapped inside 
Power Cogs.
* Clockwerk also loves to build 
Blade Mail, which will deal more damage to Pugna than Clockwerk due to Pugna's low health pool.
* Finally, both Hookshot and 
Rocket Flare can allow him to finish off Pugna out of range of his Nether Ward.
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.
Pugna
* 
Pugna's Nether Ward doesn't really hurt Meepo since he usually buys attribute items to tank up and can be killed very quickly by 4 clones. Decrepify can amplify Poof's damage should Pugna use it to avoid Meepo's right clicking.
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.
Pugna
* Heroes with channeled abilities can be interrupted by a long-range Fissure: 
Crystal Maiden, 
Witch Doctor, 
Bane, Pugna, 
Pudge.
Legion Commander
* Earthshaker's AoE stuns can save ally against Duel, forcing Legion Commander to spend Aghanim's Scepter or 
Black King Bar.
Pugna
* Pugna's low health and reliance on channeled abilities make him very vulnerable to Tusk, although Pugna can win in a straight up 1v1 later in the game.
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.
Pugna
* Heroes who rely on channeling abilities can be interrupted in teamfights by Rolling Thunder: Crystal Maiden, Pugna, Witch Doctor
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.
Pugna
* All of Pugna's damage is magical, which can get blocked by 
Fate's Edict's 100% magic resistance.
* Oracle has two abilities that apply a dispel, which can easily remove Decrepify on his ally or Oracle.
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.
Pugna
* Luna can deal constant damage to Pugna through the low-cooldown Lucent Beam and her right clicks.
* Life Drain will be always canceled by 
Lucent Beam if Pugna does not have Black King Bar.
* 
Decrepify can be suicide against Luna due to Lucent Beam and 
Eclipse.
* Nether Ward is rather weak against Luna because unlike other heroes who rely on magical damage to damage or kill enemies, yet their ablities have very high mana costs, Luna does not have abilities that cost a lot of mana and Luna mostly uses her abilities to initiate a teamfight or to finish off fleeing enemy heroes.
* Luna is a common Black King Bar carrier, which allows her to protect herself against Pugna's only-magical damage output.
Additional:
* Luna can deal constant damage to Pugna through the low-cooldown Lucent Beam and her right clicks.
* Life Drain will be always canceled by Lucent Beam if Pugna does not have Black King Bar.
* Decrepify can be suicide against Luna due to Lucent Beam and Eclipse.
* Nether Ward is rather weak against Luna because unlike other heroes who rely on magical damage to damage or kill enemies, yet have very high mana costs, she does not have abilities that cost a lot of mana and Luna mostly uses her abilities to initiate a teamfight or to finish off fleeing enemy heroes.
* Luna is a common Black King Bar carrier, which allows her to protect herself against Pugna's only-magical damage output.
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.
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.
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.
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.
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.
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.
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.
Pugna
* Both Jakiro's Ice Path and Liquid Frost can be used to cancel Life Drain from either Jakiro or an ally.
* Decrepify only makes Pugna even more vulnerable to Jakiro's magical damage, And it has no adverse effects on Jakiro himself.
* Aghanim's Scepter upgraded 
Macropyre can deal pure damage-over-time and pierce debuff immunity, which can discourage Pugna from even trying to use Life Drain.
* Bear in mind, however, that Nether Ward can do some considerable damage to Jakiro due to high mana costs on his abilities.
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.
Legion Commander
* Solar Guardian can save allies who are being dueled and will interrupt her Duel initiation.
Pugna
* Primal Beast has multiple ways to cancel Life Drain very quickly.
* Pugna has a very low strength gain and as a support does not have much gold to buy health items, making him vulnerable to Primal Beast's onslaught of magical damage.
* Ironically, Decrepify actually just increases Primal Beast's damage on the targeted ally if Trample is activated. However, it can be used to slow him down and prevent any further Trample damage.
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.
Pugna
* Puck can dodge 
Nether Blast and Life Drain with his Phase Shift, easily avoiding Pugna's strong burst magic damage.
* 
Waning Rift's silence allows Puck and its teammates to easily deal with Pugna, which cannot do the same to it, because with Puck it will be easy to avoid such an attack from the Decrepify.
* The Puck's combo: Waning Rift + 
Illusory Orb + 
Dream Coil doesn't have a huge amount of damage to feel the damage of the Pugna from Nether Ward, however, it may be quite enough to kill the Pugna solo at an early stage of the game with 
Witch Blade
Additional:
* Puck easily dodges the Nether Blast and the Pugna Life Drain with his 
Phase Shift, which is why he can easily avoid his strong magic damage
* The Puck's silence from the Waning Rift ability allows her team to easily cope with the Pugna, which cannot be said about the Pugna, because with the Puck it will be easy to avoid such an attack from the Decrepify
* The Puck's combo: Waning Rift + Illusory Orb + Dream Coil doesn't have a huge amount of damage to feel the damage of the Pugna from Nether Ward, however, it may be quite enough to kill the Pugna solo at an early stage of the game with Witch Blade
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
* 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
* 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.
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
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.
Pugna
* Heroes with magical or pure damage output will not have any problems against Atrophy Aura at all: 
Luna, 
Lina, 
Jakiro, Pugna, Bane, 
Snapfire, 
Muerta, 
Nyx Assassin, 
Enigma, 
Tinker, Witch Doctor, Zeus, Crystal Maiden.
Legion Commander
* 
Astral Imprisonment prevents Legion Commander from killing her opponents in Duels.
Additional:
* Outworld Destroyer can save an ally hero caught by 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.
Pugna
* Any heroes with high intelligence, such as Invoker and Pugna.
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.
Legion Commander
* Heroes with strong dispels can dispel Bane's disables from their allies: 
Oracle, Legion Commander, 
Omniknight.
Pugna
* Earth Spirit does not fly a small distance on 
Rolling Boulder using 
Stone Remnant, which will be a big problem for Life Drain, since Pugna will stop receiving health from breaking the distance of the ability, which will give the Earth Spirit team a chance to kill Pugna, by the way, this also works well with 
Boulder Smash, which pushes the enemy and can annoy the distance
* Earth Spirit has excellent control with a small recharge on Rolling Boulder and 
Geomagnetic Grip, which can knock down Pugna`s Life Drain, as well as completely turn him off in a fight, because he is very dependent on his abilities
* Magic damage from Earth Spirit's abilities can be disastrous for Decrepify, as it will kill him very quickly, and if Earth Spirit collects 
Ethereal Blade in such a game, it can easily destroy Pugna in one Rolling Boulder hit
* Earth Spirit also turns out to be a strong decision against Nether Ward, because he experiences it with his large amount of health, and if he collects 
Heart of Tarrasque(and 
Bracerin early game)in such a game, he may not feel it at all and calmly control Pugna with his abilities
Additional:
* Earth Spirit does not fly a small distance on Rolling Boulder using Stone Remnant, which will be a big problem for Life Drain, since Pugna will stop receiving health from breaking the distance of the ability, which will give the Earth Spirit team a chance to kill Pugna, by the way, this also works well with Boulder Smash, which pushes the enemy and can annoy the distance
* Earth Spirit has excellent control with a small recharge on Rolling Boulder and Geomagnetic Grip, which can knock down Pugna`s Life Drain, as well as completely turn him off in a fight, because he is very dependent on his abilities
* Magic damage from Earth Spirit's abilities can be disastrous for Decrepify, as it will kill him very quickly, and if Earth Spirit collects Ethereal Blade in such a game, it can easily destroy Pugna in one Rolling Boulder hit
* Earth Spirit also turns out to be a strong decision against Nether Ward, because he experiences it with his large amount of health, and if he collects Heart of Tarrasque(and Bracerin early game)in such a game, he may not feel it at all and calmly control Pugna with his abilities
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
Pugna
* Pugna is very reliant on his abilities for damage which Silencer can take advantage off. But he has to be careful around the Nether Ward as Silencer's abilities cost a lot of mana to use.
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.
Pugna
* Pugna is a very fragile hero who can easily get caught and killed by Storm Spirit's long range initiation.
* This is especially true if he has 
Orchid Malevolence or 
Scythe of Vyse.
* Pugna has no disables that can prevent Storm Spirit from escaping.
* Even though 
Ball Lightning requires high amount of mana, Nether Ward is ineffective since Storm Spirit is invulnerable while using it.
* Storm Spirit's other abilities cost very insignificant amount of mana for Nether Ward to be effective.
Pugna
* Heroes with mana burn: Nyx Assassin, Invoker, Outworld Destroyer, Pugna, Lion
Pugna
* Life Drain does not instantly kill the illusions from 
Phantasm
* 
Chaos Bolt and 
Reality Rift can easily interrupt the channeling from Life Drain.
* Reality Rift makes it harder for Pugna to keep his distance between Chaos Knight.
* Nether Ward barely deals any significant damage on Chaos Knight as Chaos Knight's abilities do not cost a lot of mana
* The overwhelming damage of Chaos Knight and his illusions will do a quick work on Pugna's poor HP pool, or safely remove the Nether Ward from the battlefield.
Legion Commander
* Heroes with strong area damage to destroy Phantasm illusions: Axe, 
Ember Spirit, Legion Commander, Phoenix
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
Pugna
* Phantom Lancer creates way too many illusions for Pugna's Life Drain to destroy, overwhelming him easily.
* 
Doppelganger can dodge Nether Blast or dispel Decrepify.
* 
Diffusal Blade is a common item for Phantom Lancer to burn Pugna's large mana pool and deals a large amount of damage in the process.
Additional:
* Though Life Drain instantly destroys illusions, Phantom Lancer creates way too many for Pugna to handle.
* A good Phantom Lancer will also dodge your Nether Blast with Doppelganger.
* Phantom Lancer is the most natural Diffusal Blade carrier to burn Pugna's very large pool of mana away and deal a large amount of damage in the process.
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.
Pugna
* Nether Blast can deal high damage to Chen and clear waves of his creeps.
* Decrepify can be used to waste the duration of 
Penitence.
* Nether Ward can discourage Chen from using Penitence, 
Holy Persuasion and 
Hand of God due to their fairly high mana costs.
* Life Drain can often kill Chen or any of his allies before he can save them with Hand of God thanks to it's high damage and low cooldown.
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.
Pugna
* Decrepify prevents 
Omnislash damage, until Juggernaut gets a 
Nullifier.
* Without a disable, Pugna's high movement speed makes it harder to chase him with 
Blade Fury.
* Juggernaut has low mana and his skills cost large amount of mana. Nether Ward will hurt him more and even worse, the damage from the ward is inflicted before the Spell immunity provided by Blade Fury.
Additional:
* Decrepify is the perfect tool against Omnislash until he gets a Nullifier, and even then he will probably waste a couple of slashes before he uses it.
* Without an extra disable, Pugna's high movement speed makes it impossible to chase him with Blade Fury.
* Unlike some other carries like 
Slark or 
Phantom Assassin, Juggernaut's spells cost a hefty amount of mana and he will seriously get hurt by Nether Ward. Don't forget the damage from the ward is inflicted before the spell immunity is provided by Blade Fury.
Legion Commander
* Duel pierces spell immunity and forces him to attack Legion Commander, making him unable to use Omnislash.
Pugna
* Pugna's Decrepify allows him to save allies from being ganked by Viper, since Viper mostly relies on direct attacks in order to deal damage.
* Nether Ward can discourage Viper from spamming his abilities.
* Viper's damage over time is not enough to kill Pugna as he will have more than enough time to save himself (or his allies) with Life Drain and Viper has no solutions to cancel it.
* Pugna has no passive abilities, which renders 
Nethertoxin nearly useless.
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.
Pugna
* As Terrorblade's damage output comes mainly from direct attacks, he will struggle greatly against heroes who have abilities that give evasion, trigger on attack or which can disarm an enemy hero: 
Centaur Warrunner, 
Hoodwink, 
Huskar, Invoker, 
Leshrac with 
Nihilism from Aghanim's Scepter, Lifestealer with Aghanim's Scepter upgraded 
Infest, 
Pangolier, Phantom Assassin, Pugna, 
Techies, 
Windranger etc.
Legion Commander
* Duel's long duration prevents Terrorblade from swapping his health with 
Sunder.
* Overwhelming Odds deals high damage to Terrorblade's illusions.
Pugna
* Decrepify can be used on allies to prevent them from attacking Axe and triggering Counter Helix during Berserker's Call. He can also cast it on Axe to prevent anyone from attacking him.
* Life Drain can be used to heal himself or allies caught in Berserker's Call, preventing them from dropping low enough for Axe to kill them with Culling Blade.
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.
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
Pugna
* Pugna easily copes on the line with the Keeper of the Light push with his Nether Blast, and in addition to Nether Ward, the Keeper of the Light is not able to throw 
Illuminate on creeps for a long time, so Pugna earns more gold and a level on the line
Additional:
* Pugna easily copes on the line with the Keeper of the Light push with his Nether Blast, and in addition to Nether Ward, the Keeper of the Light is not able to throw Illuminate on creeps for a long time, so Pugna earns more gold and a level on the line
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
* 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
Pugna
* Nether Ward discourages Tinker from using abilities and items due to its high damage against heavy mana usage.
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.
Pugna
* Any hero that can outrange Plague Ward can neutralize them without putting themselves at risk of receiving Poison Sting: Arc Warden, 
Chen, 
Clinkz, 
Drow Ranger, Lina, 
Mirana, Nature's Prophet, Pugna and 
Sniper.
* Special mention to heroes that outrange Plague Ward after obtaining talents that increase attack range.
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.
Pugna
* Pugna's Decrepify prevents the target from taking physical damage or doing damage, which poses a huge problem for Lycan, as he mainly deals physical damage.
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: 
Lycan, Arc Warden, 
Warlock, Chen
Legion Commander
* Press the Attack dispels Flaming Lasso.
* Batrider is unlikely to win a Duel in any stage of the game.
Pugna
* Amazingly, Enchantress has even lower health than Pugna. Though she does pack quite a punch through 
Impetus, she can't use it if she is under Decrepify.
* Pugna's Magical DPS is way greater than the heal from 
Nature's Attendants, which will also harm her quite a bit if she's next to Nether Ward.
Pugna
* Pugna's Decrepify can render Templar Assassin's physical attacks useless.
* Pugna can also cast Life Drain on Templar Assassin, burning her Refraction instances.
* On the other hand, Pugna generally has low health and armor. Use this to your advantage.
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.
Pugna
* Nether Blast is one of the best tower pushing abilities in the game, with a low cooldown. A competent Pugna will (at the very least) destroy tier 2 towers and make space for his team before Spectre can finally come online.
* Spectre's spells, while not spammable, have a fairly high mana cost, so Nether Ward can be fairly damaging to Spectre early game. The mana degen will also dampen Spectre's early game power significantly.
* Once Pugna gets Aghanim's Scepter, he can spam Life Drain on any illusion Spectre summons, whether it'd be from 
Haunt, 
Manta Style, or some other means.
* In addition, Pugna can disable Spectre's 
Desolate ability (although its damage is pure, it requires physical attacks) with his Decrepify ability, leaving Spectre only with 
Spectral Dagger.
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.
Pugna
* Decrepify prevents Faceless Void from attacking trapped allies inside 
Chronosphere, wasting a large portion of its duration if Faceless Void can't dispel it.
Pugna
* Nether Ward causes Death Pulse to actually damage Necrophos rather than heal him. Meanwhile, Reaper Scythe's gigantic mana cost while Necrophos is near the Nether Ward can often instantly kill him.
* Nether Blast and Life Drain both make quick work of Necrophos's small healthpool, especially during Ghost Shroud. The latter also makes him an unappealing target for Reaper's Scythe, and can often force Necrophos to use it defensively as he has no other means of interrupting his channeling.
Pugna
* Nether Ward can punish Timbersaw, as Timbersaw is a spell-caster with low cooldowns. Furthermore, Timbersaw usually appears in the midst of battle, placing himself in range of Nether Ward's Mana Flares.
* Timbersaw has no stuns or silences to stop Life Drain. Since all of Pugna's Spells are magical, the damage can be devastating to Timbersaw.
* Decrepify can further increase all the magical damage done to Timbersaw, bypassing the enhanced physical resistance he can get from 
Reactive Armor.
Additional:
* Nether Ward can punish Timbersaw, as Timbersaw is a spell-caster with low cooldowns. Furthermore, Timbersaw usually appears in the midst of battle, placing himself in range of Nether Ward's Mana Flares.
* Timbersaw has no stuns or silences to stop Life Drain. Since all of Pugna's Spells are magical, the damage can be devastating to Timbersaw, especially when combined with Decrepify.
Pugna
* Decrepify prevents Shadow Fiend from attacking for its duration, potentially preventing him from getting a kill.
* Nether Ward can do heavy damage to Shadow Fiend if he tries to cast his 
Requiem of Souls and his 
Shadowraze.
Additional:
* Decrepify prevents Shadow Fiend from attacking for its duration, potentially preventing him from getting a kill.
* Nether Ward can do heavy damage to Shadow Fiend if he tries to cast his Requiem of Souls or spam Shadowraze.
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.
Pugna
* 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
* 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.
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
Pugna
* Heroes who are reliant on physical damage will be nullified by Decrepify: Riki, Wraith King, 
Juggernaut.
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.
Pugna
* Nether Ward can do a ton of damage to Disruptor because of his high mana costs.
* Life Drain can be used to heal an ally trapped by Static Storm-Kinetic Field combo (if Pugna is not a target).
Pugna
* Nether Ward punishes Leshrac's constant mana usage from spamming spells.
* Leshrac needs to be in the thick of the fight to deal damage, and so cannot escape from Nether Blast nor Life Drain easily.
Additional:
* Leshrac needs to be close to target in order to do damage, Pugna can outrun Leshrac with ease due to his superior movement speed.
* 
Split Earth can also be hard to land on Pugna for the same reason.
* Leshrac uses huge amounts of mana to do damage, Nether Ward forces him to either not contribute in a fight or kill himself in the process.
Legion Commander
* Duel's long duration prevents Weaver from activating 
Time Lapse or escaping with 
Shukuchi.
Legion Commander
* Press The Attack 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.
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.
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.
Pugna
* Heroes with high movement speeds like Pugna and 
Meepo can run around, to, or away from Snapfire during 
Mortimer Kisses and dodge the projectiles easily due to their slow speed.
* Heroes with mobility spells (such as 
Queen of Pain's 
Blink and 
Clockwerk with Hookshot) can easily avoid 
Lil' Shredder and Mortimer Kisses.
* Heroes with high movement speeds like Pugna and Meepo can run around, to, or away from Snapfire during Mortimer Kisses and dodge the projectiles easily due to their slow speed.
Pugna
* Heroes that commonly attack ethereal units will not have any problems against Muerta's Pierce The Veil: Tinker, Jakiro, Lina, Luna, Pugna or Ogre Magi, Enigma, 
Batrider, Techies, 
Broodmother, 
Dawnbreaker, 
Shadow Shaman, Bane, Tinker, Venomancer, Arc Warden.
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
* 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.
Pugna
* Nether Blast, Decrepify and Life Drain deal high magical damage and bypasses Bulwark.
* Nether Ward reduces the amount of abilities Mars can use during fights and forces Mars to be careful about the heavy mana cost of Arena Of Blood.
* Pugna is one of few heroes that can contest Mars' ability to push and defend towers early on.
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.
Legion Commander
* Invoker's spells will disable and destroy Legion Commander while she's locked in a Duel.
Pugna
* Nether Ward on its own can greatly hinder Invoker from casting many of his abilities, at least until he gets a significant amount of HP or is under the protection of spell immunity from Black King Bar
* Life Drain provides True sight, revealing Invoker through Ghost Walk, and forcing him or his allies to use an ability or item to interrupt its channeling
* Outside of Nether Ward's range, Invoker shall have the advantage, as Invoker has Tornado to purge Pugna's Decrepify when it is used defensively, Tornado or Cold Snap to prevent Pugna from channeling Life Drain
* A poorly used Decrepify on Pugna's allies means Invoker's abilities can be used to deal more damage to them.
Additional:
* Because Invoker relies on casting a large amount of spells to contribute to fights, Nether Ward can force him to not cast anything at all or take a large amount of damage to cast spells.
Legion Commander
* Heroes with long lockdowns: Shadow Shaman, Legion Commander.
Pugna
* Any hero who can counter-initiate in anticipation without getting caught in Reverse Polarity: 
Sven, Omniknight, Enigma, Luna, Naga Siren, 
Mars, Jakiro, Venomancer, 
Elder Titan, Faceless Void, Rubick, Keeper of the Light, Pugna, Invoker, 
Spectre, 
Alchemist, Treant Protector, Lina, Oracle, Zeus, Shadow Shaman, Phoenix, 
Razor, Huskar, Batrider, 
Kunkka, 
Tidehunter, Wraith King, 
Sand King, 
Medusa, Dawnbreaker.
Legion Commander
* Heroes with long or multiple disables will prevent Legion Commander from winning Duels: Shadow Shaman, Lion
Pugna
* Nether Ward will be problematic for heavy nukers and spammers like 
Skywrath Mage, Lina, Lion and Invoker, but Pugna must not use Decrepify defensively against them as he will be helping them out more than anything.
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.
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.
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
* 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.
Pugna
* Heroes that can apply early pressure before Phantom Assassin has farm are massive threats: Axe, 
Viper, Meepo, Jakiro, Pugna, Slark, Venomancer etc.
Pugna
* Pugna's Decrepify makes sure that either Alchemist is unable to hit anyone while also being slowed and susceptible to magical damage, or can protect an ally from physical attacks. Besides, Pugna can push early on, when Alchemist is not strong enough to repel it, so by the time Alchemist comes online, he might be forced to sit in base.
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
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: Lycan, Arc Warden, Warlock, Chen
Pugna
* Nether Ward will be problematic for heavy nukers and spammers like Skywrath Mage, Lina, Lion and Invoker, but Pugna must not use Decrepify defensively against them as he will be helping them out more than anything.
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
Pugna
* Pugna: Decrepify prevent the Spirit bear from attacking or protect allies from it.
Pugna
* Heroes that can punish aggressive heroes, such as: Leshrac, Shadow Demon, Pugna, 
Death Prophet.
Legion Commander
* Magnetic Field prevents Legion Commander from getting wins with Duel.
Additional:
* 
Magnetic Field prevents Legion Commander from easily gaining wins with Duel.
Pugna
* Arc Warden can't use Magnetic Field to stall the damage of Nether Blast on towers, but he can buy 
Aghanim's Shard to diminish its damage.
* Arc Warden has no innate disables to stop Life Drain and Decrepify
* The short cooldown of both Life Drain and Decrepify also means Pugna can deal with Arc Warden and Arc Warden's clone simultaneously most of the time
* A good Pugna looks to end the match early while Arc Warden, a very item reliant hero, thrives in longer matches.
Legion Commander
* Heroes who rely on summons will see them destroyed easily by Overwhelming Odds: Lycan, Arc Warden, Warlock, Chen
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
Pugna
* Even though Pugna's low HP means that he can be quickly burst down, his Nether Ward heavily punishes casters whose spells cost a lot of mana, like Zeus. Casting 4 of his active spells, including Nimbus, close to an enhanced level 4 Nether Ward, can make the ward deal up to 1750 magical damage.
* Decrepify can further increase the damage dealt by Nether Ward upon Zeus. However, if used on Pugna himself or on one of his allies, it will amplify the damage done by Zeus' abilities.
Pugna
* Heroes who build a Black King Bar (or have any sources of spell immunity) to channel abilities/items can still get interrupted by Dismember: Enigma, Juggernaut, Phantom Assassin, Pugna, Elder Titan.
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.
Legion Commander
* Troll Warlord's melee bash and high attack speed can often help him and his allies win Duels against Legion Commander.
Pugna
* Troll Warlord can't switch targets at will, in order to build 
Fervor stacks, which makes it easy to use Decrepify in order to save allies
* During 
Battle Trance, Pugna can easily use Nether Blast, Decrepify and Life Drain on him
Pugna
* Spirit Siphon does a lot of magical damage, especially in the early game. This allows her to demolish low health heroes such as Zeus, Pugna, especially when combined with her other spells.
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.
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.
Pugna
* All of Pugna's abilities are active, making Demonic Purge break from Aghanim's Scepter useless.
* Nether Ward punishes Shadow Demon's constant mana usage from spamming spells, especially Shadow Poison.
* An attempt to save an ally using Disruption can easily become a perfect setup for a Nether Blast for the enemy.
* Life Drain can be used to heal Pugna or an ally to save them from Shadow Demon's abilities.
* However, it can be cancelled by Disruption unless Pugna buys defensive items.
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.
Pugna
* Enigma's abilities have a huge mana cost, meaning that Nether Ward will deal a lot of damage to Enigma.
* Pugna can heal allies trapped inside Black Hole thanks to Life Drain, Pugna can also damage multiple of Enigma's allies around him with Life Drain when he casts it on Aghanim's Shard upgraded Nether Ward during teamfight.
* Nether Blast can easily kill Eidolons, especially when Enigma is pushing.
* Even though Pugna cannot cancel 
Black Hole on his own, smart Pugna can buy Orchid Malevolence to stop Enigma from channeling Black Hole and make him more vulnerable to counter-attacks with Decrepify and Life Drain.
Additional:
* Enigma's abilities have a huge mana cost, meaning that Nether Ward will deal a lot of damage to Enigma.
* Pugna can heal allies trapped inside Black Hole thanks to Life Drain.
* Nether Blast can easily kill Eidolons, especially when Enigma is pushing.
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.
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.
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
* Legion Commander's Overwhelming Odds deals damage for every Treant it hits, which allows it to easily wipe out large waves of them.
Pugna
* Sniper's huge range makes him an unviable target to use Life Drain on, forcing Pugna to risk playing out of position to use it on Sniper.
* Sniper's 
Shrapnel can be used to provide vision on Nether Ward, and his range allows him to easily take it out.
* A clumsy Pugna may accidentally boost Sniper's Shrapnel and 
Assassinate damages if he recklessly uses Decrepify on himself or his allies.
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.
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.
Pugna
* Pugna can turn out to be an effective hero against Dazzle due to the fact that he does not allow him to extend his 
Poison Touch with his Decrepify, which is why Dazzle cannot keep the enemy under prolonged deceleration.
* Pugna has a very strong ability against casters with a small health reserve - Nether Ward, which is why heroes like Dazzle will not be able to constantly throw their Poison Touch 
Bad Juju and Shadow Wave at enemies under the action of Nether Ward or will be forced to take a lot of damage
Additional:
* Pugna can turn out to be an effective hero against Dazzle due to the fact that he does not allow him to extend his Poison Touch with his Decrepify, which is why Dazzle cannot keep the enemy under prolonged deceleration.
* Pugna has a very strong ability against casters with a small health reserve - Nether Ward, which is why heroes like Dazzle will not be able to constantly throw their Poison Touch Bad Juju and Shadow Wave at enemies under the action of Nether Ward or will be forced to take a lot of damage
Pugna
* Pugna only deals magical damage, which Anti-Mage is exceptionally resistant due to Counterspell.
* Anti-Mage can dispel Decrepify with Manta Style.
* Pugna has a very large mana pool. This allows Anti-Mage to constantly deal bonus damage to Pugna with Mana Break and devastate Pugna's entire team with Mana Void.
Additional:
* Since Pugna relies on his teammates for protection, it is fairly common for Anti-Mage to get multiple kills with a single use of his 
Mana Void on Pugna if he's missing a considerable portion of his mana.
* Pugna's massive mana pool will result in Anti-Mage's 
Mana Break almost always dealing the bonus damage from the mana burn.
* 
Counterspell negates a large amount of Pugna's damage, as most of Pugna's damage comes from his spells.
* 
Blink can be used to get out of a bad situation, and Pugna has no way to prevent him from casting it.
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.
Pugna
* Nether Blast's animation makes it easy to time Spiked Carapace for a stun.
* Pugna has the largest intelligence gain in the game, making him a prime target for Mana Burn.
* Pugna needs to channel Life Drain, making him easy to hit with Impale.
Additional:
* Due to Pugna's incredible intelligence growth and terrible strength growth, Nyx should always be able to take you out with his combo, with or without an added 
Dagon. 
Mind Flare will deal a large amount of damage in particular, especially in the late game.
* 
Spiked Carapace is also a great tool versus Pugna. A good player will wait for you in 
Vendetta until you farm a creep wave with Nether Blast and reflect it back at you as their initiation and setup for 
Impale.
Legion Commander
* Duel's long duration prevents Nyx Assassin escaping from Vendetta. With Aghanim's Scepter, she can also bypass Spiked Carapace.
Legion Commander
* 
Tethered heroes are much harder for Legion Commander to kill in Duels.
* 
Relocate can cancel Duels and save allies.
Legion Commander
* Duel is very effective against Io due to its low health and armor.
Legion Commander
* 
Mystic Flare can easily burst down Legion Commander while she is Dueling.
Pugna
* Due to the high mana cost of his spells and the low cool down of them, Nether Ward can seriously damage Skywrath Mage if he isn't careful.
* Skywrath Mage's fragility makes him very susceptible to Pugna's high burst damage.
Additional:
* Nether Ward will make Skywrath Mage next to useless in fights, as his low hp pool will not allow him to sustain through the damage of the ward should he choose to cast spells. Be wary though that Skywrath's huge burst will make very quick work of Pugna's low hp should the ward be destroyed, and Decrepify won't help Pugna at all.
Pugna
* Heroes with no mobility will take some good damage from Sand King's spells: 
Dragon Knight, Jakiro, Pugna, 
Earthshaker.
Pugna
* Pugna's Nether Ward damages Sand King when he channels Epicenter, preventing him from using Blink Dagger afterward.
Pugna
* Fragile heroes: Bounty Hunter has decent nuking capabilities with Shiruken Toss and Jinada thus making fragile heroes easy picks for ganking. Few examples of such heroes are:Crystal Maiden, Pugna, Skywrath Mage, 
Io, Witch Doctor, etc.
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
* 
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.
Pugna
* Pugna can save allies with both healing or by making them ethereal but needs to be careful of Sven's Aghanim's Scepter purge.
Legion Commander
* Heroes with long or multiple disables will prevent Legion Commander from winning Duels: Shadow Shaman, Lion
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
* 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".
Pugna
* Heroes who are reliant on physical damage will be nullified by Decrepify: Riki, Wraith King, Juggernaut.
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.
Pugna
* Cold Embrace is a death sentence against Pugna, since its the perfect setup for all his abilities, especially Life Drain.
* Decrepify can be cast to save the ally under Winter's Curse effect, wasting most of its duration.
* Winter Wyvern's abilities require a lot of mana, allowing Nether Ward to deal lots of damage.
Pugna
* If Ursa uses
Enrage, Pugna's Life Drain is next to worthless against him, due to Ursa taking 80% less damage, therefor Pugna heals by only 20% of the damage that the spell normally deals.
Earthshock
Skull Basher. With his high Attack Speed from 
Overpower. he can easily cancel Life Drain
Nullifier
Blink Dagger he can easily wipe you out with Overpower.
Overpower can destroy a full health 
Nether Ward and still have a few swipes leftover, Also Ursa's low mana spells means he takes negligible damage from the Nether ward anyway.
Diffusal Blade carrier, using it to both amplify his damage, but as his primary way to catch fleeing heroes
Fury Swipes stacking damage will quickly demolish them, allowing Ursa to safely switch heroes
* It also dispels Decrepify, Even if you wait until he casted it, he can still dispel it with Shard upgraded
* Ursa also commonly builds
* If Decrepify is defensivly casted, Ursa can still cast Earthshock both to slow you, and to deal amplified magic damage. He also commonly builds a
* If Ursa jumps on you with a
* Ursa's
* Ursa is also a common
* Pugna is also the primary target of Ursa, due to him being both quite squishy, and a serious threat to his team, Ursa prioritizes the weakest link as
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