Dark Seer
* A Sniper who is somewhat competent at positioning is hardly going to be affected by any of Dark Seer's spells thanks to 
Take Aim.
* However, an illusion of Sniper made with Wall of Replica is extremely powerful, and hard to deal with.
Medusa
* Sniper can outrange both Medusa's arrows and Stone Gaze, allowing him to focus her down during a teamfight.
Additional:
* Medusa is a fairly immobile hero that deals damage around her with 
Split Shot. Sniper should outrange her and should stay out of harm's way from Split Shot.
* More importantly, Sniper should have enough attack range to fire at Medusa during her 
Stone Gaze without turning to stone, so the ultimate is mostly wasted against him.
Dark Seer
* 
Fortune's End dispels Ion Shell and Surge, making any gank attempt on Dark Seer in the laning phase likely to succeed.
* 
Fate's Edict prevents all magical damage that comes from Dark Seer's abilities.
* Fortune's End dispels Ion Shell on creeps, which Dark Seer relies on to farm and zone.
Additional:
* Fortune's End can dispel 
Ion Shell, a skill that helps Dark Seer immensely in the laning phase, as well as 
Surge, a move-speed buff, effectively allowing Oracle to control Dark Seer, especially in the laning phase.
Medusa
* He can use either his own or his double's 
Flux to bypass the spellblock from Linken's Sphere, using the leftover Flux + 
Spark Wraith to slow Medusa's already low move speed to a crawl.
* Arc Warden has a farming advantage with double 
Hand of Midas, and can generally bully Medusa with other items that benefit from duplication.
Medusa
* Ursa's status resistance from 
Enrage reduces duration of Medusa's Stone Gaze.
* Ursa can stack damage with 
Fury Swipes easily against her Mana Shield in a prolonged team match.
Additional:
* Medusa's tankiness doesn't help her very much against Fury Swipes in long teamfights.
* With no escape mechanism and a slow movement speed, getting jumped on by Ursa usually spells a quick end for Medusa in the early game.
Dark Seer
* 
Flame Guard makes Dark Seer not deal any damage with his skills to Ember Spirit.
Medusa
* Fiend's Grip provides mana drain, which can heavily damage 
Mana Shield and prevent Medusa from using Stone Gaze.
* Even if she does use Stone Gaze, Nightmare can buy enough time to protect allies and reset the fight.
Additional:
* 
Fiend's Grip leaves Medusa defenseless, since not only does it deal damage, it also drains mana.
Dark Seer
* The constant dispel from Demonic Purge will make any attempt to save the victim or himself by Surge become futile. For what it's worth, Demonic Purge will also dispel Ion Shell.
Dark Seer
* 
X Marks the Spot prevents Dark Seer or his allies from escaping with Surge.
Medusa
* Silencer burns easily through her effective HP from Mana Shield, by taking away her intelligence.
* 
Arcane Curse punishes her repeatedly casting 
Mystic Snake to keep her mana pool high. He can force her to use 
Manta Style before he has cast 
Global Silence and 
Medusa usually does not want to build 
Black King Bar.
Medusa
* With 
Smoke Screen, Riki will silence and catch Medusa in a surprise with high miss chance flushing her from positions easily in team fights.
* He can deal a huge amount of damage through 
Cloak and Dagger, even through Mana Shield.
Dark Seer
* 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.
Medusa
* 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.
Dark Seer
* Heroes with AoE abilities will hit Slark in Shadow Dance: 
Lina, 
Jakiro, 
Underlord, 
Leshrac, 
Dark Seer, 
Earthshaker, 
Timbersaw, 
Crystal Maiden.
Dark Seer
* 
Spell Steal will easily steal all abilities from Dark Seer.
Additional:
* Spell Steal can perfect from Rubick's steal all abilities from Dark Seer. Rubick's always purchase 
Aghanim's Scepter can two stolens abilities from Dark Seer's and waiting for seconds for second stolen abilities (example: combinated Vacuum and Wall of Replica) and many different combination.
* A good positoning from Rubick's Spell Steal waiting steal abilities from Dark Seer 
Wall of Replica and illusion from Wall of Replica Dark Seer's can fighting with effect from outcome steal Wall of Replica from Rubick's.
* Combinated Rubick's steal Surge and 
Blink Dagger is very important catch from Dark Seer's and enemies.
* Rubick's 
Telekinesis can lifted up Dark Seer or enemy heroes and throw to Wall of Replica from Rubick's steal.
Medusa
* 
Burning Spear's damage over time can rapidly burn Medusa's mana and health alike.
* 
Inner Fire can slow and disarm Medusa and also allow Huskar to follow up with Life Break.
Medusa
* Medusa lacks mobility or escape mechanisms. 
Earth Spike and 
Hex can neutralize her strong damage potential and allow for 
Lion's team to focus her down.
* 
Mana Drain is a perfect ability to weaken Medusa's durability as it can quickly drain her Mana Shield, making her far less tanky. Mana Drain can also be used to restore mana of Lion's allies, which can nullify the mana steal from Mystic Snake.
* Mana Drain, along with Hex, destroy illusions instantly, which may be extremely helpfull and efficient against core builders of Manta Style, like Medusa herself.
Medusa
* E.M.P. allows Invoker to burn Medusa's mana to weaken Mana Shield.
* Medusa's lack of mobility makes her easy to kite with Invoker's spells.
Additional:
* 
E.M.P. is a large mana burn nuke which can hit Medusa's Mana shield with enough damage to lose even more mana.
* 
Deafening Blast disarms Medusa's ability to deal pseudo-AOE damage during teamfights.
* 
Cold Snap allows the opposing team to repeatedly stun Medusa in short succession, preventing her from successfully casting her ultimate due to its long cast time.
Medusa
* Heroes who take a long time to become strong are in for a rough mid game, such as 
Outworld Destroyer, 
Magnus, Medusa, and 
Anti-Mage.
Dark Seer
* Dark Seer's only disable is Vacuum. Though he starts off with high armor and health, he'll eventually have a hard time dealing with high mobility heroes such as 
Weaver or 
Queen of Pain.
Medusa
* Heroes that build 
Diffusal Blade or can fit it well into their item build will also make Medusa much less tanky: 
Riki, 
Naga Siren, 
Terrorblade, 
Juggernaut, 
Spectre, Slark.
Dark Seer
* 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.
Medusa
* Other heroes who has armor and slow debuffs won't allow Medusa to disengage from combat: 
Tidehunter, 
Bristleback, 
Slardar.
Dark Seer
* Dark Seer's only disable is Vacuum. Though he starts off with high armor and health, he'll eventually have a hard time dealing with high mobility heroes such as Weaver or Queen of Pain.
Dark Seer
* Abilities that deal low damage with high amounts of instances are irrelevant against Pudge during Flesh Heap's active: 
Gyrocopter's 
Rocket Barrage and Dark Seer's Ion Shell are just a couple examples.
Medusa
* Hard carries who just want to farm and be left alone will not appreciate Primal Beast, heroes such as Medusa, 
Drow Ranger...
Medusa
* Other heroes who has armor and slow debuffs won't allow Medusa to disengage from combat: Tidehunter, Bristleback, Slardar.
Dark Seer
* In general, heroes who are melee with no way to fight back can be very easily poked by Monkey King to gain his Jingu Mastery stacks: Dark Seer, Riki, 
Rubick.
Medusa
* 
Vendetta burns a significant amount of mana on hit, and the damage from the ability drains Medusa's mana pool even further.
* Due to the passive nature of Mystic Snake and Split Shot, it can possibly proc Nyx's 
Spiked Carapace if he's within range of Medusa's abilities and isn't invisible.
* Medusa lacks single target damage, making Nyx with Aghanim's Scepter extremely hard to deal with if Medusa is the team's main damage source.
Additional:
* With her passive Split Shot, Medusa can be easily interrupted by Spiked Carapace during combat, especially during her precious Stone Gaze.
* Mana Burn quickly destroys Mana Shield, especially if Medusa only increases her mana pool by bolstering intelligence (which has the added bonus of increasing Mana Burn's damage).
* Uncontrollable damage from Mystic Snake and Split Shot can trigger Spiked Carapace.
* Medusa lacks single target damage, making a Burrowed Nyx Assassin hard to kill.
Dark Seer
* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Jakiro, 
Viper, 
Venomancer, 
Huskar, 
Ember Spirit, Dark Seer, 
Sand King, 
Doom, 
Dawnbreaker. However, this also means they are easily stunned.
Medusa
* With 
Static Link, Razor can effectively make Medusa useless in teamfights by reducing her main damage output. It can, however, be blocked by a 
Linken's Sphere.
* 
Plasma Field allows Razor to get on top of Medusa, slowing her already slow movement speed to a mere crawl.
* 
Eye of the Storm capitilizes on Medusa's low armor and causes her to be very vulnerable, even through Mana Shield.
Dark Seer
* Dark Seer can increase the movement speed of allies with Surge, breaking Static Link.
Medusa
* 
Bulwark can make each of Medusa's attacks target him instead, reducing Medusa's contribution on team fights.
* 
Spear of Mars stuns Medusa and also pushes her away from teamfights, taking advantage of Medusa's low mobility.
* 
Arena Of Blood blocks Medusa's attacks from outside the arena.
Medusa
* Medusa's Stone Gaze forces Mars to choose between getting petrified, or turning his vulnerable back on Medusa.
Medusa
* Phantom Lancer with Diffusal Blade will very quickly burn Medusa's mana, making Mana Shield significantly less effective.
* 
Doppelganger's 1 second invulnerability can be used to dodge Medusa's petrification from Stone Gaze, as well as Mystic Snake.
* Phantom Lancer's illusions outnumber Medusa's targets from Split Shot, likely shielding his team in the process.
Dark Seer
* Heroes that rely on illusions typically spawn very strong illusions inside Dark Seer Wall of Replica that he can use against them or their team: 
Phantom Lancer, 
Chaos Knight, Naga Siren, Terrorblade.
Additional:
* Ion Shell helps taking down illusions quickly, making it easy to identify the real Phantom Lancer.
* Surge allows Dark Seer and his teammates to run away from Phantom Lancer, who relies on his 
Phantom Rush to chase enemies.
Dark Seer
* Dark Seer's 
Vacuum and Ion Shell can clear a wave of Chen's Creeps effectively.
* Surge applies haste movement and negates the slow from 
Penitence, allowing Dark Seer to easily escape from Chen and his creeps.
* Dark Seer's full combo from Dark Seer's Vacuum, Wall of Replica and 
Normal Punch from Aghanim's Scepter can often kill Chen or any of his allies before he can save them with 
Hand of God.
Additional:
* Dark Seer's Vacuum and Ion Shell can clear a wave of Chen's Creeps effectively.
* Surge applies haste movement and negates the slow from Penitence, allowing Dark Seer to easily escape from Chen and his creeps.
* Dark Seer's full combo from Dark Seer's Vacuum, Wall of Replica and Normal Punch from Aghanim's Scepter can often kill Chen or any of his allies before he can save them with Hand of God.
Medusa
* Medusa's Split Shot can easily kill Chen's creeps.
* Mystic Snake can quickly kill Chen's creeps and deal intense damage for every killed creep while also draining their mana with each bounce. Aghanim's Scepter upgraded Mystic Snake can also disable both, Chen and his creeps upon impact.
* Mana Shield will make it impossible for Chen to burst down Medusa.
* Stone Gaze can disable Chen from using Hand of God to save himself or his allies.
Dark Seer
* Dark Seer can take great advantage of 
Divided We Stand by putting an Ion Shell on a clone in order to harass them effectively.
* Vacuum can take a single Meepo and disable him for Dark Seer and his teammates to take out.
Medusa
* Poof won't damage Medusa and she can use Stone Gaze to disable all of Meepo's clones.
* Mystic Snake will easily become the bane of Meepo early game.
Dark Seer
* Heroes with haste can negate Enchant's slow: Weaver, Dark Seer, 
Lycan, 
Centaur Warrunner.
Medusa
* Enchantress often has a small army of neutral creeps, allowing Medusa to hit her with a later bounce of her Mystic Snake.
Dark Seer
* Certain heroes can mess up with Pangolier's positioning and timing (especially if he intends to use Rolling Thunder during combat): 
Vengeful Spirit, 
Keeper of the Light, Huskar, Dark Seer
Medusa
* Split Shot will keep attacking Pangolier even when he is rolling around.
* Stone Gaze stuns Pangolier during Rolling Thunder, or forces him to roll away.
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: 
Beastmaster, 
Broodmother, 
Enigma, 
Nature's Prophet, 
Visage, 
Warlock, 
Wraith King.
Medusa
* Medusa's Split Shot can make quick work of Enigma's Eidolons and take advantage of their considerable bounty.
* Medusa can also kill Eidolons with her Mystic Snake that can also greatly damage Enigma and drain some of his mana.
* If Medusa activates Stone Gaze at the start of a fight, it can make initiating and landing an effective 
Black Hole exceedingly difficult, because Stone Gaze can cancel Enigma's Black Hole even through spell immunity, which can discourage Enigma from even trying to initiate with Black Hole.
Additional:
* Medusa's Split Shot can make quick work of Enigma's Eidolons and take advantage of their considerable bounty.
* If Medusa activates Stone Gaze at the start of a fight, it can make initiating — and landing an effective Black Hole exceedingly difficult. Stone Gaze can cancel Enigma's Black Hole even through spell immunity, which can discourage Enigma from initiating with Black Hole.
Dark Seer
* Heroes with escape abilities: Anti-Mage Dark Seer Slark 
Storm Spirit 
Windranger Weaver can kite Lifestealer due to him having no lockdown.
Medusa
* Lifestealer's low mobility makes him easy to kite.
* Stone Gaze pierces 
Rage, wasting its cooldown and making Lifestealer unable to fight.
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: Beastmaster, Broodmother, Enigma, Nature's Prophet, Visage, Warlock, Wraith King.
Medusa
* Visage's familiars are easy targets to Split Shot.
* Mana Shield will resist Soul Assumption instances without effort.
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: Beastmaster, Broodmother, Enigma, Nature's Prophet, Visage, Warlock, Wraith King.
Medusa
* Heroes with Linken's Sphere as core item: Weaver, 
Morphling, Medusa.
Dark Seer
* With Normal Punch from Aghanim's Scepter, Dark Seer can gain an advantage against heroes who rely on evasion as Normal Punch has true strike: 
Phantom Assassin, Windranger, 
Hoodwink.
Medusa
* Heroes with disables that ignore spell immunity will render Phantom Assassin completely useless in teamfights throughout the game: 
Axe, Enigma, Vengeful Spirit, Doom, 
Bane, Beastmaster, 
Pudge, Medusa, Warlock.
Medusa
* Doom does not disable Mana Shield. As such, Doom's damage is largely mitigated by her mana shield. Additionally, Medusa is not reliant on her abilities to be effective during a teamfight, making Medusa an unproductive hero to target.
* Medusa is an ideal Linken's Sphere carrier. Should one be purchased, and without any additional disables, Doom may find that few opportunities exist to effectively lockdown, disable, and kill Medusa.
Dark Seer
* Venomancer is a low health hero and low range hero who is easy to harass with Ion Shell on a creep in the early game.
* Venomancer depends entirely on all his slows to keep distance or chase, but since Surge ignores slows, it is nearly impossible for Venomancer to hunt or run away from Dark Seer or his surged teammates.
Dark Seer
* Ion Shell destroys 
Refraction's protection stacks in short time.
* Surge ignores the massive slow from 
Psionic Trap.
Medusa
* Heroes that build Diffusal Blade or can fit it well into their item build will also make Medusa much less tanky: Riki, Naga Siren, Terrorblade, Juggernaut, Spectre, Slark.
Dark Seer
* Heroes that rely on illusions typically spawn very strong illusions inside Dark Seer Wall of Replica that he can use against them or their team: Phantom Lancer, Chaos Knight, Naga Siren, Terrorblade.
Medusa
* Medusa's Split Shot and Mystic Snake combined with 
Mjollnir, a common item for Medusa, will whittle down all of Naga Siren's illusions, including Naga Siren herself.
* Medusa's Stone Gaze can disable Naga Siren even for the duration of 
Song of the Siren and even if Naga Siren is spell immune, discouraging Naga Siren from even trying to use Song of the Siren to save herself or counter-initiate against Medusa.
Additional:
* Medusa's Split Shot and Mystic Snake combined with Mjollnir, a common item for Medusa, will whittle down all of Naga Siren's illusions, including Naga Siren herself.
* Medusa's Stone Gaze can disable Naga Siren even for the duration of Song of the Siren and even if Naga Siren is spell immune, discouraging Naga Siren from even trying to use Song of the Siren to save herself or counter-initiate against Medusa.
Medusa
* Her Mana Shield is too tough for Lycan to break.
* Mystic Snake can hit for a massive damage once it spread between his summons.
Additional:
* Can be easily petrified despite his speed.
* Summoned wolves will be targeted by Split Shot or Mystic Snake
Medusa
* Mana Shield can tank most of the damage from Reaper's Scythe; with sufficient mana, the kill threshold drops significantly.
* Necrophos has a movement speed equal to Medusa, and is easy to chase down with a slowing item in Medusa's inventory.
Medusa
* Should Luna choose to buy Manta Style, Medusa will be able to kill illusions from them with Split Shot and Mjollnir, which is a common item on Medusa.
* Mystic Snake allows Medusa to easily harass Luna and steal mana from her, preventing Luna from retaliating with 
Lucent Beam.
* Medusa can survive 
Eclipse thanks to Mana Shield, which can cause Luna to struggle greatly in bursting down Medusa and force her to buy Diffusal Blade and it's upgrade 
Disperser.
* Even with Black King Bar, Medusa's Stone Gaze will still be able to disable Luna, which could even discourage her from counter-initiating with Eclipse.
* For the same reasons, Medusa makes a very powerful ally for Luna when they are in the same team.
Additional:
* Should Luna choose to buy Manta Style, Medusa will be able to kill illusions from them with Split Shot and Mjollnir, which is a common item on Medusa.
* Mystic Snake allows Medusa to easily harass Luna and steal mana from her, preventing Luna from retaliating with Lucent Beam.
* Medusa can survive Eclipse thanks to Mana Shield, and since Luna is not a hero that often goes for Diffusal Blade, she will struggle greatly in bursting down Medusa.
* Even with Black King Bar, Medusa's Stone Gaze will still be able to disable Luna, which could even discourage her from counter-initiating with Eclipse.
* For the same reasons, Medusa makes a very powerful ally for Luna when they are in the same team.
Medusa
* If Medusa activates Stone Gaze before Spirit Breaker reaches her with Charge of Darkness, the charge will inevitably fail.
* Medusa has three ways to counter Spirit Breaker's Charge of Darkness: Stone Gaze can disable Spirit Breaker's Charge of Darkness if he faces Medusa directly. Aghanim's Scepter upgraded Mystic Snake can disable Spirit Breaker and cancel his Charge of Darkness if it hits him. And 
Cold Blooded provided by 
Aghanim's Shard that can cast a single-targeted Mystic Snake at Spirit Breaker if he uses Charge of Darkness on her.
* Mana Shield and overall tankiness allows Medusa to easily survive Spirit Breaker's initiation. And to make things worse, Spirit Breaker is not a common Diffusal Blade nor Disperser wielder to counter this problem at all.
* Overall, any attempt for Spirit Breaker to gank and kill Medusa will hurt him more than the other way around.
Medusa
* Split Shot can destroy Tombstone Zombies and Tombstone itself while still damaging heroes.
Medusa
* Mana Shield makes Medusa very hard to take down in Duels.
* Stone Gaze stops Legion Commander from Dueling altogether, regardless of who she targets.
Dark Seer
* 
Living Armor can be destroyed quickly with Ion Shell.
Medusa
* Any long duration disables that can pierce through both, Pierce The Veil and Black King Bar are devastating against Muerta: Enigma's Black Hole, Dawnbreaker's 
Solar Guardian, Axe's 
Berserker's Call, Naga Siren's Aghanim's Scepter upgraded 
Ensnare and 
Reel In from Aghanim's Scepter, Jakiro's Aghanim's Scepter upgraded 
Macropyre, Bane's Fiend's Grip, Pudge's 
Dismember, 
Batrider's 
Flaming Lasso, Beastmaster's 
Primal Roar, 
Grimstroke's 
Soulbind, Medusa's Stone Gaze, Magnus's 
Reverse Polarity.
Dark Seer
* With Normal Punch from Aghanim's Scepter, Dark Seer can gain an advantage against heroes who rely on evasion as Normal Punch has true strike: Phantom Assassin, Windranger, Hoodwink.
Medusa
* 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.
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: Beastmaster, Broodmother, Enigma, Nature's Prophet, Visage, Warlock, Wraith King.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: Lina, Zeus.
Dark Seer
* Heroes that rely on illusions typically spawn very strong illusions inside Dark Seer Wall of Replica that he can use against them or their team: Phantom Lancer, Chaos Knight, Naga Siren, Terrorblade.
Medusa
* Heroes that are hard to gank: Axe, 
Death Prophet, Phantom Lancer, Slark, Centaur Warrunner, Bristleback, Medusa, Mars.
Dark Seer
* With Normal Punch from Aghanim's Scepter, Dark Seer can gain an advantage against heroes who rely on evasion as Normal Punch has true strike: Phantom Assassin, Windranger, Hoodwink.
Dark Seer
* Heroes who do not have nor rely on passive abilities make Nethertoxin much less effective: 
Clinkz, Pugna, Nature's Prophet, Dark Seer, Lycan, 
Tusk
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: Beastmaster, Broodmother, Enigma, Nature's Prophet, Visage, Warlock, Wraith King.
Additional:
* Surge allows for Dark Seer and his allies to escape from Upheaval due to it ignoring any slow.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: Lina, Zeus.
Dark Seer
* The haste provided by Dark Seer's Surge or a {Rune:Haste} renders Lich's slows ineffective.
Dark Seer
* Heroes that rely on summons will suffer against Ion Shell, which kills them very quickly: Beastmaster, Broodmother, Enigma, Nature's Prophet, Visage, Warlock, Wraith King.
Dark Seer
* Heroes without blink mechanisms or spell immunity will have a hard time positioning against 
Pit of Malice: Sven, 
Tiny, Wraith King, 
Dragon Knight, 
Meepo, Doom, 
Bounty Hunter, Dark Seer, 
Undying, Alchemist, 
Legion Commander.
Dark Seer
* Heroes with strong area-of-effect damaging and/or disabling abilities will be able to intercept Underlord and his team when they exit from Fiend's Gate: Luna's Aghanim's Scepter upgraded Eclipse, Dawnbreaker's Solar Guardian, Axe's Berserker's Call, Mars's Arena of Blood, Jakiro's Macropyre, 
Dual Breath and 
Ice Path, Naga Siren's Song of the Siren, Razor's Eye of the Storm and Plasma Field, Lina's 
Light Strike Array, Broodmother's 
Spinner's Snare from Aghanim's Scepter, Elder Titan's 
Earth Splitter and 
Echo Stomp, Alchemist's 
Unstable Concoction and 
Acid Spray, Queen of Pain's 
Sonic Wave, Dark Seer's Wall of Replica and Vacuum, Venomancer's 
Noxious Plague and 
Poison Nova from Aghanim's Scepter, Oracle's Fortune's End and 
Rain of Destiny from Aghanim's Shard, 
Bloodseeker's 
Blood Rite, Enigma's Black Hole and 
Midnight Pulse, 
Shadow Fiend's 
Requiem of Souls, Batrider's Aghanim's Scepter upgraded Flaming Lasso, 
Firefly, 
Flamebreak and 
Sticky Napalm, 
Ancient Apparition's 
Ice Blast, Sand King's 
Epicenter, 
Sand Storm and 
Burrowstrike, Gyrocopter's 
Call Down, Ember Spirit's 
Sleight of Fist, Death Prophet's 
Exorcism and 
Silence, 
Monkey King's 
Wukong's Command, Crystal Maiden's 
Freezing Field, 
Muerta's 
The Calling, Medusa's Stone Gaze, Zeus's 
Nimbus from Aghanim's Scepter. 
Dark Willow's 
Bramble Maze, 
Pangolier's 
Swashbuckle, Grimstroke's Soulbind, 
Ink Swell and 
Stroke of Fate, Earthshaker's 
Echo Slam and 
Fissure, 
Puck's 
Dream Coil and 
Waning Rift, 
Winter Wyvern's 
Winter's Curse, Magnus's Reverse Polarity.
Medusa
* Heroes with strong area-of-effect damaging and/or disabling abilities will be able to intercept Underlord and his team when they exit from Fiend's Gate: Luna's Aghanim's Scepter upgraded Eclipse, Dawnbreaker's Solar Guardian, Axe's Berserker's Call, Mars's Arena of Blood, Jakiro's Macropyre, Dual Breath and Ice Path, Naga Siren's Song of the Siren, Razor's Eye of the Storm and Plasma Field, Lina's Light Strike Array, Broodmother's Spinner's Snare from Aghanim's Scepter, Elder Titan's Earth Splitter and Echo Stomp, Alchemist's Unstable Concoction and Acid Spray, Queen of Pain's Sonic Wave, Dark Seer's Wall of Replica and Vacuum, Venomancer's Noxious Plague and Poison Nova from Aghanim's Scepter, Oracle's Fortune's End and Rain of Destiny from Aghanim's Shard, Bloodseeker's Blood Rite, Enigma's Black Hole and Midnight Pulse, Shadow Fiend's Requiem of Souls, Batrider's Aghanim's Scepter upgraded Flaming Lasso, Firefly, Flamebreak and Sticky Napalm, Ancient Apparition's Ice Blast, Sand King's Epicenter, Sand Storm and Burrowstrike, Gyrocopter's Call Down, Ember Spirit's Sleight of Fist, Death Prophet's Exorcism and Silence, Monkey King's Wukong's Command, Crystal Maiden's Freezing Field, Muerta's The Calling, Medusa's Stone Gaze, Zeus's Nimbus from Aghanim's Scepter. Dark Willow's Bramble Maze, Pangolier's Swashbuckle, Grimstroke's Soulbind, Ink Swell and Stroke of Fate, Earthshaker's Echo Slam and Fissure, Puck's Dream Coil and Waning Rift, Winter Wyvern's Winter's Curse, Magnus's Reverse Polarity.
Medusa
* Heroes that build Diffusal Blade or can fit it well into their item build will also make Medusa much less tanky: Riki, Naga Siren, Terrorblade, Juggernaut, Spectre, Slark.
Dark Seer
* Dark Seer's Vacuum and Ion Shell allows him to clear a wave of Terrorblade's illusions.
* Because Terrorblade often builds items that require 
Ultimate Orb like Manta Style and 
Eye of Skadi, Dark Seer can create a very strong illusion of Terrorblade with Wall of Replica and Normal Punch from Aghanim's Scepter.
* If Dark Seer can use Vacuum to help teammates land their AoE abilities, Terrorblade will be quickly killed before he even gets a chance to use Sunder.
Additional:
* Dark Seer's Vacuum and Ion Shell allows him to clear a wave of Terrorblade's illusions.
* Because Terrorblade often builds items that require Ultimate Orb like Manta Style and Eye of Skadi, Dark Seer can create a very strong illusion of Terrorblade with Wall of Replica and Normal Punch from Aghanim's Scepter.
* If Dark Seer can use Vacuum to help teammates land their AoE abilities, Terrorblade will be quickly killed before he even gets a chance to use Sunder.
Dark Seer
* Heroes with fast movement abilities will suffer huge damage when afflicted by Rupture: 
Spirit Breaker, 
Earth Spirit, Dark Seer.
Additional:
* 
Rupture can deal a lot of damage to either a surged Dark Seer or his allies and prevent the target from getting into position.
Medusa
* Mana Shield makes it very difficult for Bloodseeker to gain his Thirst bonuses.
* Rupture rarely kills Medusa through Mana Shield.
Dark Seer
* Strong laners are usually at a disadvantage because of how well Sven can jungle. Heroes such as Dark Seer. Underlord and Legion Commander may find that later Sven takes care of them very quickly after some jungle farming.
Medusa
* Stone Gaze allows Medusa to easily kite and kill Sven.
* Mana Shield negates much of Sven's burst damage.
Additional:
* Mana Shield makes it very hard for Sven to burst her within Storm Hammer's stun duration.
* Stone Gaze makes it very difficult for Sven to fight Medusa at any stage of the game.
* Mystic Snake can slow Sven down enough for allies to capitalize on his commitment in a fight.
Medusa
* Heroes that build Diffusal Blade or can fit it well into their item build will also make Medusa much less tanky: Riki, Naga Siren, Terrorblade, Juggernaut, Spectre, Slark.
Dark Seer
* Dark Seer can pull together Spectre's illusions with Vacuum, and Wall of Replica creates an illusion of Spectre that deals massive damage.
Medusa
* Other heroes who has armor and slow debuffs won't allow Medusa to disengage from combat: Tidehunter, Bristleback, Slardar.
Medusa
* Medusa cares less than other heroes about armor reduction, since Mana Shield blocks 70% of all damage without taking armor/magic resistance into consideration. This makes 60% of your Corrosive Haze ineffective until Medusa's mana is drained.
Medusa
* Heroes with extremely slow movement speed will cripple against Solar Bind: Medusa, Viper
Additional:
* 
Will-O-Wisp will keep Medusa busy after she got hit by 
Blinding Light.
Dark Seer
* Heroes with hastes: Dark Seer, Lycan
Medusa
* Webbed areas can be used to hit and run, covering distance hastily weakening her on the way and initiating ganks.
* Even though Medusa can hunt down Spiderlings easily when given enough range, 
Silken Bola will cause her attacks to miss and get her swarmed in no time.
* Medusa usually does not build a Black King Bar to benefit from Mana Shield fully while Broodmother can fit a Diffusal Blade to burn away all of Medusa's mana.
Additional:
* 
Spin Web will allow Broodmother to pick her own fights and sometimes slip away to ambush Medusa.
* Though Medusa's Split Shot and Mystic Snake can help Medusa deal with Broodmother's spiderlings, Broodmother will create too much of them for her to handle, allowing her to outnumber Medusa's targets from Split Shot and shield her team in process.
Dark Seer
* Ion Shell zones out Broodmother in the laning phase, and can kill her spiderlings if used on one Spiderling in a group.
* Vacuum can pull Broodmother out of the treeline.
Additional:
* Ion Shell is a very powerful weapon against Broodmother's Spiderlings and makes her laning much harder.
Medusa
* Axe can take advantage of Medusa's awfully low HP to insta-kill her with 
Culling Blade, making it extremely difficult for her to farm for items to compensate for the lack of strength during early and mid-game while Axe is continuously harassing around.
Medusa
* Mana Shield reduces the effectiveness of Counter Helix.
* Stone Gaze makes it very difficult for Axe to initiate on Medusa and her allies.
Dark Seer
* Dark Seer's strength lies in his high-mana cost skills. So
Mana Break can be a great nuisance for him, since it can reduce his mana and prevent him from casting his spells.
Mana Void can deal a lot of damage if Dark Seer spent a lot of mana on his abilities.
*
Medusa
* Anti-Mage easily destroys
Mana Shield with Mana Break, especially once he has 
Manta Style.
Stone Gaze with Blink, and can reinitiate after its duration is over.
Mana Break burns Medusa's mana easily, especially when coupled with a 
Manta Style.
Blink, burning her mana or forcing her to use Stone Gaze.
Mana Void is effective against Medusa's big mana pool and mana usage, presenting a huge hazard to Medusa's allies around her since her Mana Shield still gives her some protection if she has mana.
* Anti-Mage effectively avoids
Additional:
*
* Can easily initiate on Medusa with
*