Beastmaster
* 
Illuminate clears Beastmaster's summons and is effective against his push.
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.
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.
Additional:
* Beastmaster's summons and 
Inner Beast are very useful to attack his cursed teammate.
* Cold Embrace effectively mitigates 
Primal Roar's single-target initiation on allies.
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.
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
* 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.
Beastmaster
* Having many summons out will cause 
Echo Slam to deal extra damage.
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
* 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
* 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.
Medusa
* Anti-Mage easily destroys Mana Shield with Mana Break, especially once he has Manta Style.
* Anti-Mage effectively avoids Stone Gaze with Blink, and can reinitiate after its duration is over.
Additional:
* 
Mana Break burns Medusa's mana easily, especially when coupled with a Manta Style.
* Can easily initiate on Medusa with 
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Beastmaster
* Heroes with Linken's Sphere as core item: 
Weaver, 
Morphling, Medusa.
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 summoned units don't fare well against Dawnbreaker. (
Phantom Lancer ,Beastmaster ,
Lycan).
Medusa
* Other heroes who has armor and slow debuffs won't allow Medusa to disengage from combat: 
Tidehunter, 
Bristleback, 
Slardar.
Beastmaster
* Heroes who summon multiple units that are not spell immune. Nature's Prophet,Lycan,Beastmaster
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.
Medusa
* Other heroes who has armor and slow debuffs won't allow Medusa to disengage from combat: Tidehunter, Bristleback, Slardar.
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.
Beastmaster
* Heroes with Linken's Sphere as core item: Weaver, Morphling, Medusa.
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.
Beastmaster
* Single-target disablers will have difficulty locking down a Chaos Knight with Phantasm active: 
Bane, Beastmaster, 
Bloodseeker, 
Clockwerk, 
Doom, 
Shadow Shaman.
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.
Beastmaster
* Heroes with summons or illusions can counter Flux, such as Beastmaster , 
Chen, or 
Shadow Demon.
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.
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.
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.
Beastmaster
* Primal Roar takes Sven out of the fight completely, even with Black King Bar.
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.
Beastmaster
* Primal Roar allows Beastmaster to keep Lycan in place after he used his Shapeshift.
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
Beastmaster
* Heroes with disables that go through spell immunity can end Bloodseeker before he has the chance to do anything: 
Batrider, Beastmaster
Medusa
* Mana Shield makes it very difficult for Bloodseeker to gain his Thirst bonuses.
* Rupture rarely kills Medusa through Mana Shield.
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's
Meat Hook.
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.
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.
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.
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.
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.
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.
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.
Beastmaster
* 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.
Medusa
* Heroes that are hard to gank: Axe, 
Death Prophet, Phantom Lancer, Slark, 
Centaur Warrunner, Bristleback, Medusa, 
Mars.
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.
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
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.
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.
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.
Beastmaster
* Primal Roar and the slow from Boars make kiting Tiny very easy.
Beastmaster
* Wild Axes destroys large amounts of trees specially upgraded with Aghanim's Scepter,
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
* Primal Roar and the slow from Boars make kiting Troll Warlord very easy.
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
* 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
* Mana Shield makes Medusa very hard to take down in Duels.
* Stone Gaze stops Legion Commander from Dueling altogether, regardless of who she targets.
Beastmaster
* Inner Beast helps Beastmaster's team destroy 
Supernova quickly.
Medusa
* Split Shot can destroy Tombstone Zombies and Tombstone itself while still damaging heroes.
Beastmaster
* Attacks from Boars and the attack speed boost from Inner Beast will quickly wear down 
Refraction.
Beastmaster
* Beastmaster's Hawk can find Tinker easily while he is pushing or blinking into trees.
Medusa
* Lifestealer's low mobility makes him easy to kite.
* Stone Gaze pierces 
Rage, wasting its cooldown and making Lifestealer unable to fight.
Medusa
* Visage's familiars are easy targets to Split Shot.
* Mana Shield will resist Soul Assumption instances without effort.
Beastmaster
* Wraith King's lack of area of effect spells makes him easily overwhelmed by Beastmaster's summons.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: 
Lina, 
Zeus.
Beastmaster
* Illusion or summon-based heroes can be a problem to Viper due to his lack of AoE damage: Naga Siren, Phantom Lancer, Beastmaster
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.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, Queen of Pain.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, Queen of Pain.
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.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: Lina, Zeus.
Beastmaster
* Heroes with illusions and summons can manfight Night Stalker: Terrorblade, Beastmaster, Broodmother.
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.
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.
Medusa
* Mana Shield reduces the effectiveness of Counter Helix.
* Stone Gaze makes it very difficult for Axe to initiate on Medusa and her allies.
Beastmaster
* Heroes who relies on illusions and summons (Beastmaster, Chaos Knight, etc.).
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.
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.
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.
Medusa
* Enchantress often has a small army of neutral creeps, allowing Medusa to hit her with a later bounce of her Mystic Snake.
Beastmaster
* Heroes with AoE abilities are a bane to Beastmaster's summons: Storm Spirit, Magnus, Pangolier.
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.
Beastmaster
* Heroes with AoE abilities are a bane to Beastmaster's summons: Storm Spirit, Magnus, Pangolier.
Beastmaster
* Heroes who rely on high mobility are especially vulnerable to Primal Roar: Storm Spirit, Ember Spirit, Queen of Pain.
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.
Beastmaster
* Primal Roar and the slow from Boars makes kiting Ursa very easy.
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.
Beastmaster
* Heroes with strong dispels can remove Primal Roar's stun:
Abaddon, 
Slark, 
Oracle.
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.