Beastmaster
* Heroes who summon multiple units that are not spell immune. 
Nature's Prophet,
Lycan,
Beastmaster
Io
* Io is a hero who needs to be close to it's tethered target to make it effective, and that's where Leshrac gets the advantage thanks to many of his area-of-effect abilities.
* 
Lightning Storm will usually hit both Io and its tethered target since both will be close enough for the lightning to jump.
* 
Diabolic Edict and 
Pulse Nova hit all units near Leshrac, meaning he can do colossal damage to both, Io and its tethered target.
Additional:
* Lightning Storm will usually hit both Io and his 
Tethered target since both will be close enough for the lightning to jump. It can then be followed up by Split Earth.
* Diabolic Edict and Pulse Nova hit all units near Leshrac, meaning he can do colossal damage to Io and his Tethered target.
Beastmaster
* Heroes with Linken's Sphere as core item: 
Weaver, 
Morphling, 
Medusa.
Io
* Heroes that are hard to gank: 
Axe, 
Death Prophet, 
Phantom Lancer, 
Slark, 
Centaur Warrunner, 
Bristleback, Medusa, 
Mars.
Beastmaster
* Heroes with summoned units don't fare well against Dawnbreaker. (Phantom Lancer ,Beastmaster ,Lycan).
Io
* Heroes whose abilities can affect multiple enemies at once: 
Dawnbreaker, 
Ember Spirit, 
Lina, 
Luna, 
Jakiro, 
Leshrac, 
Invoker, 
Muerta, 
Dazzle.
Beastmaster
* Single-target disablers will have difficulty locking down a Chaos Knight with Phantasm active: 
Bane, Beastmaster, 
Bloodseeker, 
Clockwerk, 
Doom, 
Shadow Shaman.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, 
Broodmother, 
Chaos Knight, Lycan, 
Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, 
Terrorblade, 
Visage, 
Warlock, 
Wraith King.
Beastmaster
* Heroes with strong dispels can remove Primal Roar's stun: 
Abaddon, Slark, 
Oracle.
Io
* 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.
Beastmaster
* 
Primal Roar can be instantly dispelled by Aphotic Shield.
* The debuffs from 
Wild Axes and 
Poison from 
Call of the Wild: Boar can also be dispelled by Aphotic Shield.
Additional:
* 
Aphotic Shield effectively nullifies Primal Roar's single-target initiation on allies.
* Even being initiated by Primal Roar, 
Borrowed Time can make Abaddon extremely difficult to kill.
Beastmaster
* 
False Promise effectively nullifies Primal Roar's single-target initiation on allies.
* 
Purifying Flames kills Beastmaster's Hawk instantly and Boar with two casts.
Io
* Lich's 
Chain Frost forces Io to either give up providing buff to his ally with Tether or suffer devastating damage with his Tethered ally.
* Lich can easily use 
Sinister Gaze to disable Io from getting away with Tether or 
Relocate.
Io
* 
Living Armor and 
Leech Seed can be used to save a hero from a Relocate gank.
* 
Overgrowth can be used to cancel escape attempts with Relocate.
* Once Treant Protector buys 
Aghanim's Scepter, he will gain access to 
Eyes in the Forest, that will allow him to enchant a tree which will grant him unobstructed vision in that location, allowing him to keep his allies alerted on Io and his Tethered's attempts to gank them, and which can also allow Overgrowth to damage them and root them if they are within a 800 radius of an tree affected by Eyes in the Forest.
Io
* 
Lucent Beam can be used to cancel both, Tether and Relocate.
* Like with Leshrac's Diabolic Edict, Lightning Storm and Pulse Nova abilities. Luna's 
Moon Glaives and 
Eclipse abilities can make short work of Io and its tethered ally, particularly when upgraded with Aghanim's Scepter.
Additional:
* Lucent Beam and 0.25s Eclipse Lucent Ministun talent for Eclipse can be used to cancel both, Tether and Relocate.
* Luna's Moon Glaives and Eclipse abilities can make short work of Io and its tethered ally, particularly when upgraded with Aghanim's Scepter.
Io
* Fireblast is a good tool to interrupt Io during its escapes through Tether.
* Ignite can be one of the few spells with enough total damage to out-trade the sustained healing Io provides for its fellow laner.
* However, picking other supports that focus less on the laning phase is generally a better choice against Io.
Io
* Ice Blast prevents Io from healing an ally with Tether and prevents healing from 
Overcharge
* Io is a common 
Mekansm builder which is useless if he is affected by Ice Blast.
Additional:
* 
Ice Blast prevents Io from healing the target.
* Ancient Apparition can easily harass Io on lane with 
Chilling Touch due to it's high range and damage. This can get even worse if Ancient Apparition buys Aghanim's Scepter and combines it with items that can give him bonus attack damage and attack speed.
* Chilling Touch combined with 
Ice Vortex makes it nearly impossible for Io to escape from 
Cold Feet. Ice Vortex can also make Io and it's tethered target more vulnerable to Ancient Apparition and his allies's magical damage.
Io
* 
Strafe, 
Tar Bomb and 
Burning Barrage from 
Aghanim's Shard allow Clinkz to quickly kill Io due to its low armor.
* Clinkz iz a hero that very often goes for 
Orchid Malevolence, and its upgrade 
Bloodthorn. Alternatively, Clinkz also loves to buy 
Gleipnir. And if Clinkz has both of them, he will be able to root and silence Io and prevent him from escaping with either Tether or Relocate.
Io
* Disruptor can always Glimpse back Io or his target after he Relocated nearby.
* Even better, thanks to the indicator on the ground, you can even preemptively drop Static Storm and Kinetic Field on the spot they will relocate to.
* Thunder Strike and Glimpse are also good tools to bring back an Io that Tethered away in the fog of war.
Additional:
* 
Glimpse directly negates Relocate.
* 
Kinetic Field prevents Io from escaping with Tether.
* 
Static Storm can silence and damage both, Io and it's tethered target. And it can also mute both, Io and it's tethered target when upgraded with Aghanim's Scepter.
Beastmaster
* 
Illuminate clears Beastmaster's summons and is effective against his push.
Io
* 
Charge of Darkness can be used to escape or counter-initiate against a Relocate gank.
* 
Greater Bash and 
Nether Strike is devastating due to Io's low armor, and can even knock it away from his Tethered target.
Beastmaster
* Having many summons out will cause 
Echo Slam to deal extra damage.
Beastmaster
* 
Frostbite kills boars instantly on the laning stage leading to either experience lead or disabling Beastmaster from using Boar
* 
Crystal Nova nukes and slows down the attack and movement speed of Beastmaster's summons.
* 
Freezing Field grants improved self armor, nukes and slows down Beastmaster and his summons.
Beastmaster
* 
Reactive Armor is very effective against Beastmaster's summons during laning stage and entire game.
* Timbersaw can quickly clear Beastmaster's summons with his nukes.
* 
Lotus Orb item for Timbersaw can releases roar from the target position, stunning and damaging Beastmaster and knocking away, damaging and slowing allies that stand on the way.
Io
* Jakiro's area-of-effect ability arsenal allows him to affect multiple heroes at once, giving Io difficulties in saving them as he can only heal one hero at a time with Tether.
* 
Ice Path can be used to cancel both, Tether and Relocate.
* Jakiro commonly buys 
Rod of Atos that can be used to cancel Relocate, prevent Io in escaping with Tether and make Io easy target for Ice Path and 
Macropyre.
Additional:
* Jakiro's area-of-effect ability arsenal allows him to affect multiple heroes at once, giving Io difficulties in saving them as he can only heal one hero at a time with Tether.
* Ice Path can be used to cancel both, Tether and Relocate.
* Jakiro commonly buys Rod of Atos that can be used to cancel Relocate, prevent Io in escaping with Tether and make Io easy target for Ice Path and Macropyre.
Io
* 
Ensnare and 
Song of the Siren can be used to cancel both, Tether and Relocate and to close the distance on Io.
* 
Rip Tide combined with illusions from 
Mirror Image often finish off Io before he can save himself with Tether or Relocate.
* 
Spirits's weak area-of-effect makes it a bad tool to deal with Naga Siren's illusions from Mirror Image.
* Once Naga Siren buys Aghanim's Scepter, she can gain access to 
Reel In, which not only allows her to cancel both, Tether and Relocate, but also to pull Io to herself and her team while he is affected with Ensnare, similarly to Batrider's 
Flaming Lasso.
* Aghanim's Shard upgraded Song of the Siren can also heal the hero Io and his Tethered targed try to gank.
Additional:
* Ensnare and Song of the Siren can be used to cancel both, Tether and Relocate and to close the distance on Io.
* Rip Tide combined with illusions from Mirror Image often finish off Io before he can save himself.
* Spirit's weak area-of-effect makes it a bad tool to deal with Naga Siren's illusions from Mirror Image.
* Once Naga Siren buys Aghanim's Scepter, she can gain access to Reel In, which not only allows her to cancel both, Tether and Relocate, but also to pull Io to herself and her team while he is affected with Ensnare, similarly to Batrider's Flaming Lasso.
* Aghanim's Shard upgraded Song of the Siren can also heal the hero Io and his tethered targed try to gank.
Io
* 
Poison Touch allows Dazzle to harass both, Io and it's tethered target on lane. Aghanim's Shard upgraded Poison Touch can also hex both, Io and it's tethered target, preventing them from escaping with Relocate, and also disarming them, silencing them, muting them and rendering them helpless against Dazzle and his allies.
* Io's damage output is one of the weakest, therefore Dazzle will have plenty of time to save an ally with 
Shallow Grave from gank by Io and it's tethered target.
* 
Shadow Wave will always hit both, Io and it's tethered target if they are near the ally Dazzle uses Shadow Wave on, while healing Dazzle's allies near them. Aghanim's Scepter upgraded Shadow Wave can bounce on both, Io and it's tethered target, causing them both to take damage and to be attacked by Dazzle. And unlike Io who doesn't get healed while using Tether, Shadow Wave will always heal Dazzle no matter on which of his allies he uses it on.
* 
Bad Juju will cause both, Io and it's tethered target to lose armor every time Dazzle casts a spell while strengthening armor of Dazzle's allies.
Additional:
* Poison Touch allows Dazzle to harass both, Io and it's Tethered target on lane. Aghanim's Shard upgraded Poison Touch can also hex both, Io and it's Tethered target, preventing them from escaping with Relocate, and also disarming them, silencing them, muting them and rendering them helpless against Dazzle and his allies.
* Io's damage output is one of the weakest, therefore Dazzle will have plenty of time to save an ally with Shallow Grave from gank by Io and it's Tethered target.
* Shadow Wave will always hit both, Io and it's Tethered target if they are near the ally Dazzle uses Shadow Wave on, while healing Dazzle's allies near them. Aghanim's Scepter upgraded Shadow Wave allows Dazzle Shadow Wave directly on Io and it's Tethered target which can also bounce on both, Io and it's tethered target, causing them both to take damage and to be attacked by Dazzle. And unlike Io who doesn't get healed while using Tether, Shadow Wave will always heal Dazzle no matter on which of his allies he uses it on.
* Bad Juju will cause both, Io and it's tethered target to lose armor every time Dazzle casts a spell while strengthening armor of Dazzle's allies.
Io
* 
Homing Missile can be used to cancel escape attempts with Relocate.
* 
Flak Cannon allows Gyrocopter to attack both, Io and his Tethered target, especially when upgraded with Aghanim's Scepter.
* 
Rocket Barrage and 
Call Down allow Gyrocopter to deal serious damage to both Io and his Tethered target.
Additional:
* Homing Missile can be used to cancel escape attempts with Relocate.
* Flak Cannon allows Gyrocopter to attack both, Io and his Tethered target, especially when upgraded with Aghanim's Scepter.
* Rocket Barrage and Call Down allow Gyrocopter to deal serious damage to both Io and his Tethered target.
Io
* 
Quill Spray is very effective against Io, as it has very low armor and has to stay close to the fight to not break its Tether.
Io
* Soulbind can target both Io and its Tethered ally, allowing Grimstroke and his team to target both with single target spells. Should Io try to Relocate, Phantom's Embrace can stop its channel to prevent escape.
Additional:
* Grimstroke can catch Io and his Tethered ally easily with 
Soulbind as Io has a tendency to Tether himself with an ally frequently, which also makes them easier targets for Soulbind.
* Io is highly vulnerable to disables. Hence, Grimstroke's 
Phantom's Embrace is a great ability to hinder Io's potential.
Io
* Terrorblade can easily take advantage of Io's weak durability with 
Reflection and 
Metamorphosis.
* As Io relies on boosting his and his Tethered target's attack speed with Overcharge, Terrorblade can take advantage of this with Reflection, which can damage and slow both, Io and his Tethered target.
* Spirits's weak area-of-effect makes it a bad tool to deal with Terrorblade's illusions from 
Conjure Image and 
Manta Style.
* Io's damage output is one of the weakest, therefore Terrorblade will have plenty of time to save himself with 
Sunder.
* However, Terrorblade has no way of stopping Io to escape with Tether or to stop both, Io and his Tethered target to escape with Relocate besides 
Terror Wave from Aghanim's Scepter.
Additional:
* Terrorblade can easily take advantage of Io's weak durability with Reflection and Metamorphosis.
* As Io relies on boosting his and his Tethered target's attack speed with Overcharge, Terrorblade can take advantage of this with Reflection, which can damage and slow both, Io and his Tethered target.
* Spirits's weak area-of-effect makes it a bad tool to deal with Terrorblade's illusions from Conjure Image and Manta Style.
* Io's damage output is one of the weakest, therefore Terrorblade will have plenty of time to save himself with Sunder.
* However, Terrorblade has no way of stopping Io to escape with Tether or to stop both, Io and it's Tethered target to escape with Relocate besides Terror Wave from Aghanim's Scepter.
Beastmaster
* 
Untouchable negates Inner Beast's attack speed bonus, making her hard to kill even if stunned by Primal Roar.
* Enchantress can also take control of Beastmaster's summons.
Additional:
* 
Enchant can control Beastmaster's boars with Enchant, mitigating his effectiveness during the laning stage and teamfights.
Io
* Batrider's Flaming Lasso can be used to cancel Io's attempts to escape with Relocate and drag him away from his Tethered target. And since Io doesn't like buying 
Linken's Sphere, he will be always vulnerable to Batrider's initiations.
* Io's tendency to stick close to it's Tethered target can make Io and it's target vulnerable to Batrider's harrasing.
* Aghanim's Scepter upgraded Flaming Lasso allows Batrider to catch and drag two heroes at once, not just one. Which can potentially turn Io's Tether against him.
Additional:
* Batrider's Flaming Lasso can be used to cancel Io's attempts to escape with Relocate and drag him away from his Tethered target. And since Io doesn't like buying Linken's Sphere, he will be always vulnerable to Batrider's initiations.
* Io's tendency to stick close to it's Tethered target can make Io and it's target vulnerable to Batrider's harrasing.
* Aghanim's Scepter upgraded Flaming Lasso allows Batrider to catch and drag two heroes at once, not just one. Which can potentially turn Io's Tether against him.
Io
* 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.
Io
* 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.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* Heroes that are hard to gank: Axe, Death Prophet, Phantom Lancer, Slark, Centaur Warrunner, Bristleback, Medusa, Mars.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, 
Nyx Assassin, Phantom Assassin, Skywrath Mage, 
Tinker, 
Ursa, Void Spirit.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Io
* Squishy heroes (Io, Crystal Maiden, Lina...), as Earth Spirit can deal tons of damage with Magnetize.
Io
* 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.
Beastmaster
* 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.
Beastmaster
* Heroes with AoE abilities are a bane to Beastmaster's summons: Storm Spirit, 
Magnus, 
Pangolier.
Beastmaster
* Heroes with AoE abilities are a bane to Beastmaster's summons: Storm Spirit, Magnus, Pangolier.
Io
* 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.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, 
Queen of Pain.
Io
* Heroes that are hard to gank: Axe, Death Prophet, Phantom Lancer, Slark, Centaur Warrunner, Bristleback, Medusa, Mars.
Io
* Heroes whose abilities can affect multiple enemies at once: Dawnbreaker, Ember Spirit, Lina, Luna, Jakiro, Leshrac, Invoker, Muerta, Dazzle.
Beastmaster
* Heroes with Linken's Sphere as core item: Weaver, Morphling, Medusa.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Io
* Heroes that are hard to gank: Axe, Death Prophet, Phantom Lancer, Slark, Centaur Warrunner, Bristleback, Medusa, Mars.
Io
* 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.
Beastmaster
* Heroes with Linken's Sphere as core item: Weaver, Morphling, Medusa.
Io
* Heroes with the ability to heal allies will not be able to heal heroes affected by 
Doom: 
Chen, Dazzle, Io, Oracle, 
Omniknight, Witch Doctor, 
Winter Wyvern, Abaddon, etc.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* 
Thirst allows Bloodseeker to see where Io relocated to, should either Io or the tethered hero have low health.
* 
Rupture forces Io to stay in place, preventing it from using the Tether bonus movement speed to escape.
Beastmaster
* Heroes with disables that go through spell immunity can end Bloodseeker before he has the chance to do anything: 
Batrider, Beastmaster
Io
* 
Phantom Strike allows Phantom Assassin jump directly to Io.
* 
Coup de Grace can make a short work of Io's low health and armor.
Beastmaster
* 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.
Io
* 
Take Aim and 
Assassinate allow Sniper to reach Io even if it stays in the backline.
Io
* Heroes with high mobility can approach Sniper: 
Anti-Mage, Earth Spirit, Io, Nature's Prophet, Pangolier, 
Puck, Queen of Pain and most notably Riki.
Beastmaster
* Inner Beast helps Beastmaster's team destroy 
Supernova quickly.
Io
* Phoenix's limit AoE, damage-over-time abilities give Io plenty of time to save allies with Relocate.
Beastmaster
* Because only one clone needs to be killed in order to kill Meepo, heroes that excel at singling out enemies can also be a detriment to him, such as Batrider, Beastmaster, Pudge and Clockwerk.
Io
* Tether helps Io escape from Earthbind even if Meepo has Blink Dagger.
* Io's Spirits can pressure Meepo while laning and will usually hit at least one of his clones.
Beastmaster
* Wild Axes, Primal Roar and 
Drums of Slom can deal high damage to Chen and clear waves of his creeps.
* Even though Chen can take control of the Boar from 
Call of the Wild Boar at any time with 
Holy Persuasion, which could put Beastmaster in a disadvantage against Chen. Skilled Beastmaster can buy 
Helm of the Overlord to regain control of it to counter this problem.
* Smart Beastmaster can also buy Bloodthorn to prevent Chen from taking control of the Boar from Call of the Wild Boar and make Chen more vulnerable to Beastmaster.
Beastmaster
* The Hawk can easily find Monkey King while he is sitting on a tree.
* Wild Axes can knock out Monkey King from tree.
* Boars drastically reduce Monkey King's attack speed, making it harder for him to gain 
Jingu Mastery stacks.
Additional:
* Wild Axes can chop down trees, making it difficult for Monkey King to utilize Tree Dance well.
* 
Call of the Wild Hawk can scout Monkey King when he is perched on top of trees.
* Primal Roar can stun Monkey King for a lengthy duration even with spell immunity.
Beastmaster
* Wild Axes destroys large amounts of trees specially upgraded with Aghanim's Scepter,
Beastmaster
* Primal Roar takes Sven out of the fight completely, even with 
Black King Bar.
Beastmaster
* Attacks from Boars and the attack speed boost from Inner Beast will quickly wear down 
Refraction.
Beastmaster
* Primal Roar and the slow from Boars make kiting Tiny very easy.
Beastmaster
* Primal Roar and the slow from Boars make kiting Troll Warlord very easy.
Io
* Tether and Overcharge makes it much harder for Pudge to kill a target with 
Meat Hook, and Relocate can save the Io's ally while 
Dismember is being channeled.
Io
* Drow Ranger's lack of escape abilities makes her an easy target for Relocate ganks.
Io
* Io can escape from Pit of Malice with Tether or Relocate.
* Relocate can counter Dark Rift's split pushing.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, Queen of Pain.
Beastmaster
* Illusion or summon-based heroes can be a problem to Viper due to his lack of AoE damage: Naga Siren, Phantom Lancer, Beastmaster
Beastmaster
* Long ranged disables, especially those that pierce spell immunity, cancel Black Hole: Beastmaster's Primal Roar, Bane's 
Fiend's Grip, 
Faceless Void's 
Chronosphere, Magnus's 
Reverse Polarity, Axe's 
Berserker's Call, Pudge'sMeat Hook.
Io
* Heroes with abilities that can save teammates are also effective such as 
Shadow Demon, Dazzle, Oracle, Bane, Pugna, Tusk, Winter Wyvern, Io, 
Underlord, 
Treant Protector and 
Keeper of the Light.
Beastmaster
* Heroes who relies on illusions and summons (Beastmaster, Chaos Knight, etc.).
Beastmaster
* Heroes with summons or illusions can counter Flux, such as Beastmaster , Chen, or Shadow Demon.
Beastmaster
* Heroes with illusions and summons can manfight Night Stalker: Terrorblade, Beastmaster, Broodmother.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Io
* Nature's Prophet is extremely easy to gank with Relocate while he's split pushing.
* Tether on a friendly unit can destroy Nature Prophet's trees should he surround himself with 
Sprout as a defense.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Beastmaster
* Primal Roar allows Beastmaster to keep Lycan in place after he used his Shapeshift.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Beastmaster
* Primal Roar and the slow from Boars makes kiting Ursa very easy.
Io
* Heroes with both illusions and summons, for Io has nothing to deal with multiple enemies at once outside from Spirits's weak area-of-effect: Beastmaster, Broodmother, Chaos Knight, Lycan, Naga Siren, Nature's Prophet, Phantom Lancer, Shadow Shaman, Terrorblade, Visage, Warlock, Wraith King.
Beastmaster
* Wraith King's lack of area of effect spells makes him easily overwhelmed by Beastmaster's summons.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Beastmaster
* Beastmaster's Hawk can find Tinker easily while he is pushing or blinking into trees.
Io
* Heroes whose abilities can affect multiple enemies at once: Dawnbreaker, Ember Spirit, Lina, Luna, Jakiro, Leshrac, Invoker, Muerta, Dazzle.
Beastmaster
* 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.
Beastmaster
* Heroes with AoE abilities are a bane to Beastmaster's summons: Storm Spirit, Magnus, Pangolier.
Beastmaster
* Heroes with other kind of disables that pierce spell immunity can hold Pangolier in place during Rolling Thunder: Axe, Beastmaster, Enigma, Magnus, Pudge, Batrider, Bane, Winter Wyvern
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, Queen of Pain.
Io
* Heroes with either magical, physical or pure damage burst: Bane, Ember Spirit, Leshrac, Lina, Luna, Nyx Assassin, Phantom Assassin, Skywrath Mage, Tinker, Ursa, Void Spirit.
Beastmaster
* Skywrath Mage also has a terrible time fighting against anything that isn't a hero. His skills are mostly target-based and he has terrible strength and agility, he can easily be kited or harassed by illusion-based heroes like Chaos Knight and Phantom Lancer, or by Heroes that summon other units like 
Lone Druid, Lycan and Beastmaster.
Io
* Heroes that are hard to gank: Axe, Death Prophet, Phantom Lancer, Slark, Centaur Warrunner, Bristleback, Medusa, Mars.
Beastmaster
* 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.
Io
* 
Duel is very effective against Io due to its low health and armor.
Io
* Tethered heroes are much harder for Legion Commander to kill in Duels.
* Relocate can cancel Duels and save allies.
Beastmaster
*
Cold Embrace mitigates Primal Roar's single-target initiation on allies.
Winter's Curse can turn Beastmaster's summons and Inner Beast against his teammate.
Inner Beast are very useful to attack his cursed teammate.
Primal Roar's single-target initiation on allies.
*
Additional:
* Beastmaster's summons and
* Cold Embrace effectively mitigates
Io
*
Cold Embrace can render the extra attack speed from 
Overcharge meaningless.
Splinter Blast and 
Winter's Curse are very affective against Io, as it has to stay close to his 
Tethered target.
*