Lich
* Heroes that depend on disrupting fights with ability combos or big ultimate abilities are vulnerable to the long stun of Fiend's Grip: 
Disruptor, 
Death Prophet, 
Enigma, 
Faceless Void, 
Invoker, 
Lich, 
Magnus, 
Mars, 
Medusa, 
Outworld Destroyer, 
Phoenix, 
Puck, 
Queen of Pain, 
Shadow Fiend, 
Treant Protector, 
Underlord, 
Winter Wyvern, 
Witch Doctor, 
Zeus.
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.
Lich
* Lich is heavily reliant on his abilities to contribute to team fights, so be wary of enemies that can Silence: 
Bloodseeker, Death Prophet, 
Silencer, 
Drow Ranger, 
Skywrath Mage.
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.
Lich
* Anti-Mage can withstand magical burst damage much better than other carries, making him effective against nukers: Lich, 
Necrophos, 
Oracle, and 
Leshrac.
Additional:
* Although he can be effective against Anti-Mage in an aggro offlane, Lich has a hard time nuking down Anti-Mage in the midgame due to his Counterspell.
* All of Lich's abilities are also targeted, which makes it much harder to disable Anti-Mage.
* In the lategame, Anti-Mage can easily pick off Lich with 
Blink, and the high mana cost of Chain Frost along with Lich's large mana pool makes him vulnerable to 
Mana Void.
* Blink allows Anti-Mage to escape Chain Frost.
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.
Lich
* Vulnerable spellcasters with no escape mechanisms are easy targets for Huskar: Lich, 
Crystal Maiden, Silencer, 
Keeper of the Light, 
Venomancer, etc.
Additional:
* Lich is going to have a hard time nuking Huskar because of his high health regeneration from 
Berserker's Blood.
* Lich is a squishy support without an escape mechanism, making Lich an easy kill thanks to 
Life Break and 
Burning Spear.
* Once Huskar has 
Armlet of Mordiggian, even a maxed out Frost Blast will struggle to finish Huskar off.
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
* 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.
Lich
* Weaver doesn't care much about Lich's slows thanks to 
Shukuchi.
* If he sees Chain Frost is targeting him, he can easily isolate himself with Shukuchi so that it stops bouncing around.
* Unless Lich bursts Weaver immediately, Lich has no hard disables or silences to prevent him from using 
Time Lapse.
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.
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.
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
* 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.
Lich
* Queen of Pain can easily escape Chain Frost thanks to 
Blink.
* His low survivability makes an easy kill for 
Shadow Strike, 
Scream of Pain & 
Sonic Wave.
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
* 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.
Lich
* Chain Frost can bounce to the treants that Nature's Prophet summons.
* Nature's Prophet's 
Sprout can be used to isolate and burst down the squishy Lich.
Additional:
* His treants can prevent 
Chain Frost from jumping to Nature's Prophet or his allies.
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.
Lich
* Heroes who lack burst damage will have a hard time against Mars: 
Phantom Lancer, 
Nature's Prophet, Lich.
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.
Lich
* Heroes with low health: Lich, Crystal Maiden, Lion.
Lich
* The haste provided by 
Dark Seer's 
Surge or a {Rune:Haste} renders Lich's slows ineffective.
Lich
* Lich is heavily reliant on his abilities to contribute to team fights, so be wary of enemies that can Silence: Bloodseeker, Death Prophet, Silencer, Drow Ranger, Skywrath Mage.
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.
Lich
* Lich is heavily reliant on his abilities to contribute to team fights, so be wary of enemies that can Silence: Bloodseeker, Death Prophet, Silencer, Drow Ranger, Skywrath Mage.
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.
Lich
* Lich is heavily reliant on his abilities to contribute to team fights, so be wary of enemies that can Silence: Bloodseeker, Death Prophet, Silencer, Drow Ranger, Skywrath Mage.
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.
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.
Lich
* Heroes with powerful nuke can waste their precious abilites on her Refraction during a ganking attempt or chaos combat: Lich, 
Lina, 
Sniper, Outworld Destroyer Zeus
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.
Lich
* Phantom Assassin can easily escape Lich's slows with 
Phantom Strike.
* Phantom Assassin's 
Coup De Grace can be used to burst down the squishy Lich.
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.
Lich
* Lich does not pose a big threat to Zeus in teamfights, as his spells don't have great cast range and Zeus should be too far back for a Chain Frost to bounce among him and his allies.
* Lich has a low health pool, allowing Zeus to burst him down quickly.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: Lina, Zeus.
Lich
* 
Poof combo puts all of the Meepos very close together, making them vulnerable to Frost Blast's AoE slow and multiple bounces from Chain Frost.
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.
Lich
* Heroes with nukes: Bane, Lich, Lion, Skywrath Mage
Medusa
* Enchantress often has a small army of neutral creeps, allowing Medusa to hit her with a later bounce of her Mystic Snake.
Lich
* 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.
Medusa
* Heroes that are hard to gank: Axe, Death Prophet, Phantom Lancer, Slark, 
Centaur Warrunner, Bristleback, Medusa, Mars.
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.
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.
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.
Lich
* Lich's constant slows with 
Frost Blast and Chain Frost will slow Dragon Knight to a crawl, especially in a crowded teamfight.
Lich
* Lich's Chain Frost, especially after obtaining its respective talent that provides unlimited bounces, can take out all of Chaos Knight's illusions quickly.
* An Aghanim's Scepter-upgraded Sinister Gaze can hypnotize Chaos Knight and his illusions while also draining his already low mana pool.
Additional:
* Chain Frost can eliminate Chaos Knight's 
Phantasm army, especially after he clumped up using 
Reality Rift.
* Frost Shield will heavily reduce his army's effectiveness.
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.
Lich
* Frost Blast and Chain Frost can kite Troll Warlord effectively.
* 
Frost Shield can single-handedly waste most of the duration of Battle Trance, due to the extreme resistance to physical damage Frost Shield provides. In addition, Troll Warlord is incapable of switching targets during Battle Trance, so he cannot pick an easier target.
* Troll Warlord has little to no ability to regenerate HP, so Frost Blast together with Frost Shield can harass him effectively.
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
* 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.
Medusa
* Split Shot can destroy Tombstone Zombies and Tombstone itself while still damaging heroes.
Medusa
* Lifestealer's low mobility makes him easy to kite.
* Stone Gaze pierces 
Rage, wasting its cooldown and making Lifestealer unable to fight.
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.
Lich
* Chain Frost can deliver high amounts of damage to Lone Druid itself and his bear if they do not separate fast from each other.
Additional:
* Chain Frost will bounce between Lone Druid and his bear, forcing them to separate or suffer high amounts of damage.
Lich
* Frost Shield helps offset the armor reduction from Natural Order.
Medusa
* Visage's familiars are easy targets to Split Shot.
* Mana Shield will resist Soul Assumption instances without effort.
Medusa
* Heroes with Linken's Sphere as core item: 
Weaver, 
Morphling, Medusa.
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.
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.
Medusa
* Heroes with a lot of burst damage, especially those who rely on casting spells: Lina, Zeus.
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.
Lich
* Heroes with large magical AoE damage will fare well against Omniknight: Lich, Ancient Apparition, Jakiro, Disruptor.
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.
Lich
* Heroes with low health will die easily during Duels, and can be farmed for damage in the early game: Crystal Maiden, Lich, 
Techies, Rubick
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.
Lich
* Lycan doesn't care much about Lich's slows thanks to 
Shapeshift.
* Chain Frost can bounce to the wolves that Lycan summons.
Additional:
* Lich possesses a lot of slows, which Lycan doesn't care about when he Shapeshifts.
* Lich has no in-built escape, which makes him a good target for Lycan.
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
* 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
* Hard carries who just want to farm and be left alone will not appreciate Primal Beast, heroes such as Medusa, Drow Ranger...
Lich
* Supports who can slow him to the point Trample does very little damage in the lane are also not fun: Lich, 
Ogre Magi, Winter Wyvern.
Lich
* Bloodseeker is not affected by slows when he is affected by 
Thirst.
* If he sees Chain Frost is targeting him, he can easily isolate himself with the movement speed buff from Thirst so that it stops bouncing around.
* Lich heavily relies on his abilities to contribute to team fights, making Blood Rite effective against him.
Medusa
* Mana Shield makes it very difficult for Bloodseeker to gain his Thirst bonuses.
* Rupture rarely kills Medusa through Mana Shield.
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.
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.
Lich
* Chain Frost can deliver high amounts of damage to Arc Warden and his double if they do not separate fast from each other.
Lich
* Support heroes with low mobility can be slowed further by Incapacitating Bite, and swarmed by Spiderlings for an easy kill:
Shadow Shaman, 
Visage, 
Dazzle, 
Rubick, 
Lich.
Additional:
* Chain Frost can bounce to the Spiderlings that Broodmother spawns.
Medusa
* Webbed areas can be used to hit and run, covering distance hastily weakening her on the way and initiating ganks.
Silken Bola will cause her attacks to miss and get her swarmed in no time.
Mana Shield fully while Broodmother can fit a 
Diffusal Blade to burn away all of Medusa's mana.
Spin Web will allow Broodmother to pick her own fights and sometimes slip away to ambush Medusa.
* Even though Medusa can hunt down Spiderlings easily when given enough range,
* Medusa usually does not build a Black King Bar to benefit from
Additional:
*
* 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.