* Even though Wraith King can easily get a chance to retaliate with Reincarnation after Luna uses Eclipse against him, smart Luna can also turn Reincarnation against him by using Eclipse right after Reincarnation triggers and gets on cooldown, giving Luna an element of surprise she can use against Wraith King.
* Moon Glaives can be used to clear the waves of Wraith King's skeleton warriors summoned from Vampiric Spirit.
Additional:
* Even though Wraith King can easily get a chance to retaliate with Reincarnation after Luna uses Eclipse against him, smart Luna can also turn Reincarnation against him by using Eclipse right after Reincarnation triggers and gets on cooldown, giving Luna an element of surprise she can use against Wraith King.
* Moon Glaives can be used to clear the waves of Wraith King's skeleton warriors summoned from Vampiric Spirit.

* Even though Nyx Assassin can easily kill Luna with his high burst damage, Luna can also do the same to him if he is not careful.
* Lucent Beam can deal a fair amount of damage to Nyx Assassin if he has no Spiked Carapace available to use. Although Luna should be patient using Lucent Beam on Nyx Assassin when he uses Spiked Carapace.
* As Luna commonly buys Black King Bar, she can use it to freely attack Nyx Assassin whenever he tries to defend himself with Spiked Carapace during teamfights. Luna can also buy Eye of Skadi and Manta Style to survive Nyx Assassin's burst damage and distract him.
* Though Vendetta can deal serious damage to Luna and avoid Eclipse, smart Luna will always buy Dust of Appearance to provide vision on Nyx Assassin to her and her team.
Additional:
* Even though Nyx Assassin can easily kill Luna with his high burst damage, Luna can also do the same to him if he is not careful.
* Lucent Beam can deal a fair amount of damage to Nyx Assassin if he has no Spiked Carapace available to use. Although Luna should be patient using Lucent Beam on Nyx Assassin when he uses Spiked Carapace.
* As Luna commonly buys Black King Bar, she can use it to freely attack Nyx Assassin whenever he tries to defend himself with Spiked Carapace during teamfights. Luna can also buy Eye of Skadi and Manta Style to survive Nyx Assassin's burst damage and distract him.
* Though Vendetta can deal serious damage to Luna and avoid Eclipse, smart Luna will always buy Dust of Appearance to provide vision on Nyx Assassin to her and her team.

* Wraithfire Blast is quite predictable, and players with good reflexes will disjoint it with Blade Fury.
* Omnislash with Diffusal Blade & Aghanim's Scepter can prevent Wraith King from reincarnating unless he has his Aghanim's Shard that removes the mana cost from Reincarnation.

* Blade Fury makes Juggernaut immune to all Nyx's abilities, except Vendetta.
* Omnislash. and Swiftslash can burst Nyx down, ignoring Spiked Carapace. However, Vendetta can be used to escape, canceling Omnislash/Swiftslash.
Additional:
* Juggernaut's entire skillset greatly counters Nyx Assassin's Spiked Carapace, his most important ability.
* Blade Fury allows Juggernaut to freely attack Nyx Assassin, and deal heavy damage to Nyx Assassin. Nyx Assassin cannot counter Blade Fury with Spiked Carapace because Blade Fury gives Juggernaut spell immunity. And besides Vendetta, Nyx Assassin has no other way of dealing damage to Juggernaut while he is spell immune.
* Healing Ward allows Juggernaut to recover himself and his allies from Nyx Assassin's damage output.
* Omnislash and Swiftslash from Aghanim's Scepter can quickly finish off Nyx Assassin, and just like Blade Fury, Nyx Assassin cannot counter neither Omnislash and Swiftslash from Aghanim's Scepter with Spiked Carapace because both abilities render Juggernaut invulnerable. And if Nyx Assassin has no Vendetta available to use for escaping, both abilities will kill him very quickly before he can do anything.
* Overall, any attempt for Nyx Assassin to gank and kill Juggernaut will hurt Nyx Assassin more than Juggernaut.

* Mana Break quickly eats away at Wraith King's small mana pool, preventing Reincarnation from triggering.
* Wraith King has no innate mobility. Even with Blink Dagger, Wraith King is easily kited by Blink.
* Anti-Mage can farm much more quickly than Wraith King, allowing Anti-Mage to overpower Wraith King once a significant farm advantage is established.
Additional:
* Mana Break can prevent Wraith King from reincarnating unless Wraith King has his Aghanim's Shard that removes the mana cost from Reincarnation.
* With Manta Style, his mana burning will triple because illusions can also use Mana Break.

* Heroes who build mana boosting items but have low mana regeneration are especially vulnerable against Mana Break and Mana Void: Timbersaw, Slark, Shadow Fiend, Clinkz, Bristleback Nyx Assassin, Magnus

* Broodmother can easily clear Wraith King's skeletons with Spawn Spiderlings and summon spiderlings in their place.
* With Diffusal Blade, Broodmother can prevent Wraith King from reincarnating unless Wraith King has his Aghanim's Shard.

* Heroes with very little to no area-of-effect abilities will struggle greatly against Broodmother: Sniper, Phantom Assassin, Nyx Assassin, Bane, Visage, Bounty Hunter.

* Diffusal Blade lets Phantom Lancer drain Wraith King's mana, preventing Reincarnation from triggering until he buys an Aghanim's Shard.
* Wraith King is bad against illusions-based heroes, as Wraithfire Blast is his only single-target disable and can get overwhelmed easily.
* Doppelganger can disjoint Wraithfire Blast.
Additional:
* Doppelganger disjoints Wraithfire Blast.
* Wraith King is not good at handling illusion-based heroes, as his only disable is single-target.
* Phantom Lancer tends to get Diffusal Blade, leaving Wraith King no mana to reincarnate.

* Nyx Assassin's skillset is mostly single-targeted, therefore he will have difficulties against heroes with illusions and summons: Naga Siren, Broodmother, Lycan, Visage, Phantom Lancer. And to make things worse, Nyx Asassin is not a common Battle Fury, Maelstrom, Mjollnir, Gleipnir or Radiance wielder to counter this problem.

* Heroes with single-target abilities will be overwhelmed by Lycan and his summons: Wraith King, Bane, Phantom Assassin.

* Lycan's high health allows him to easily shrug off Nyx Assassin's burst damage and fend him off.
* As Lycan commonly buys Black King Bar, he can use it to freely attack Nyx Assassin and chase after him with Shapeshift.

* Heroes with area dispel can kill multiple skeletons at once: Brewmaster, Oracle.

* Cyclone from Storm in Primal Split can waste Nyx's Spiked Carapace, since its duration is shorter than the Cyclone's.

* Dark Pact, if timed correctly, can dispel Wraithfire Blast's stun and slow.
* Since Wraith King has a lot of health and multiple lives, Slark can keep gaining Essence Shift stacks, increasing armor, damage, and attack speed and can beat down Wraith King twice.
* Slark sometimes carries Diffusal Blade to burn mana as an attempt to shut down Reincarnation.
* Because Wraith King has no AoE abilities, Shadow Dance is particularly useful against Wraith King.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* Jakiro's area-of-effect abilities make him strong against heroes who rely on illusions and summons: Terrorblade, Naga Siren Chaos Knight, Phantom Lancer, Broodmother, Nature's Prophet, Lycan, Wraith King, Visage.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* Heroes with summons and illusions such as Broodmother and Naga Siren, are ill-suited for Wraith King to fight, as he has no source of waveclear.

* Nyx Assassin's skillset is mostly single-targeted, therefore he will have difficulties against heroes with illusions and summons: Naga Siren, Broodmother, Lycan, Visage, Phantom Lancer. And to make things worse, Nyx Asassin is not a common Battle Fury, Maelstrom, Mjollnir, Gleipnir or Radiance wielder to counter this problem.

* 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.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Fiend's GAte to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Fiend's GAte to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* Even though Visage's Familiars from Summon Familiars are fragile and can be killed quickly with Nyx Assassin's high burst damage, they can deal many instances of damage quickly, minimizing the effectiveness of Spiked Carapace.
* Gravekeeper's Cloak and tanky item builds make Visage hard for Nyx to kill with his burst damage. Aghanim's Shard upgraded Gravekeeper's Cloak also allows Visage to use Stone Form to both recover himself and stun Nyx Assassin if he is close enough to Visage.
* Visage's long range on Soul Assumption and Grave Chill make him hard to escape from, and Soul Assumption's low cooldown outmatches Spiked Carapace.

* Wraith King has no form of AoE to clear Chaos Knight's illusions from Phantasm.
* Wraith King is very vulnerable if he reincarnates in the middle of his illusions.

* Riki is a natural Diffusal Blade carrier, and it doesn't help that he's easily capable of sneaking up on Wraith King due to Cloak and Dagger.
* Riki can use Smoke Screen on top of Wraith King as he is reincarnating, making him a sitting duck for his second life. In addition, the blind prevents Wraith King from landing critical hits from Mortal Strike.
* Wraithfire Blast is quite predictable, and if Riki can react fast, he will disjoint it with Tricks of the Trade. There is also a chance he will become invisible again as the projectile travels, disjointing it.

* Like with Juggernaut's Blade Fury, Rage allows Lifestealer to freely attack Nyx Assassin and hunt him down if Vendetta is on cooldown. Nyx Assassin cannot counter Rage with Spiked Carapace because Rage gives Lifestealer spell immunity. And besides Vendetta, Nyx Assassin has no other way of dealing damage to Lifestealer while he is spell immune.
* Open Wounds from Aghanim's Shard allows Lifestealer to severely slow down Nyx Assassin while also allowing his team to recover themselves while attacking Nyx Assassin. Open Wounds can also fester and spread if Nyx Assassin takes enough damage that will trigger the spread while he is affected with Open Wounds.
* Infest combined with an ancient creep makes Nyx Assassin an easy target to surprise with Dust of Appearance or a Gem of True Sight. And similarly to Juggernaut's Omnislash and Swiftslash from Aghanim's Scepter, Aghanim's Scepter upgraded Infest can also allow Lifestealer to infest, disarm and freely attack Nyx Assassin from within. and Nyx Assassin cannot counter this with Spiked Carapace because Lifestealer is invulnerable while attacking the infested enemy hero from within.
* Like with Juggernaut, any attempt for Nyx Assassin to gank and kill Lifestealer will hurt Nyx Assassin more than Lifestealer.

* Centaur's low Intelligence makes Mind Flare do low damage.
* With some creative skill builds, Centaur's Hoof Stomp stun duration should always last longer than Spiked Carapace stun, so escaping unscathed is hard for Nyx.
* With Blink Dagger and detection, Centaur can devastate Nyx in the open.
* However, bear in mind that Nyx can also easily initiate on Centaur Warrunner as well if he uses Spiked Carapace in anticipation, and with Vendetta. The damage from Retaliate will be reflected back to Centaur Warrunner, stunning him with no chance to react after he's revealed himself, and should guarantee a successful Impale.

* A well-timed Berserker's Call can expose Nyx Assassin while he is invisible with Vendetta, and prevent him from using Spiked Carapace.
* Axe can use Battle Hunger's damage over time to minimialize effects of Spiked Carapace.
* Axe's high health also allows him to easily shrug off Nyx Assassin's burst damage and fend him off. Especially since Axe is a common Heart of Tarrasque wielder, which can completely eliminate any chance for Nyx Assassin to kill Axe alone.
* Culling Blade can often kill Nyx Assassin as he is very fragile and vulnerable to damage while Spiked Carapace is on cooldown.
Additional:
* A well-timed Berserker's Call can expose Nyx Assassin while he is invisible with Vendetta, and prevent him from using Spiked Carapace.
* Axe can use Battle Hunger's damage over time to minimialize effects of Spiked Carapace.
* Axe's high health also allows him to easily shrug off Nyx Assassin's burst damage and fend him off. Especially since Axe is a common Heart of Tarrasque wielder, which can completely eliminate any chance for Nyx Assassin to kill Axe alone.
* Culling Blade can often kill Nyx Assassin as he is very fragile and vulnerable to damage while Spiked Carapace is on cooldown.

* Wraith King has no ability to destroy trees from Tree Dance.
* Monkey King tends to get Diffusal Blade, leaving Wraith King no mana to reincarnate unless Wraith King has his Aghanim's Shard.
* A reincarnated Wraith King is an ideal target for Wukong's Command.

* Wraith King has a very low mana pool and is extremely dependant on it to cast his high mana cost abilities, so Mana Drain will make him struggle way too hard, even not being able to active his passive ability Reincarnation, forcing the Wraith King to buy Aghanim's Shard as soon as possible.
* Althought Wraith King may not be as fragile to struggle against Lion's damage, it's much easier to disable and harass him, as Wraith King doesn't have any mobility at all, his only gap closer being Wraithfire Blast which costs too much mana for his mana pool, and may only affect one target.
Additional:
* While not being able to confront Wraith King by himself, Lion's Mana Drain helps in draining Wraith King's mana, preventing him from reincarnating unless he has his Aghanim's Shard.
* Lion's Earth Spike and Hex provide decent lockdown against Wraith King as well, preventing the latter from benefiting from Vampiric Spirit bonuses.

* Wraith King's lack of area of effect spells makes him easily overwhelmed by Beastmaster's summons.

* Dragon Knight's heavy armor negates Vendetta's burst physical damage. His large HP pool also gives him a good chance of surviving Nyx Assassin's follow-up nuke damage.

* Meepo has a better advantage in farm with Divided We Stand, as well as having a higher attack speed due to his tendency to build items that give attributes. In addition, Wraithfire Blast stuns only one target, and choosing to engage one Meepo will most certainly mean engaging them all.

* Nyx Assassin's Vendetta can be revealed easily by Corrosive Haze

Additional:
* Corrosive Haze hinders Nyx Assassin's ganking attempts with Vendetta, as well as reducing his armor and make him very vulnerable due to his low health pool.

* Clinkz, Sniper, Lone Druid, Troll Warlord, Legion Commander and Wraith King are some of the Heroes that base themselves on attacks with little or no spell power, so they suffer in the grassy hands of Overgrowth.

* Heroes with area dispel can kill multiple skeletons at once: Brewmaster, Oracle.

* Heroes that have a weak laning stage: Spectre, Nyx Assassin, Clockwerk, Spirit Breaker, Omniknight, Pudge.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.

* Many physical-only single-target heroes like Lifestealer, Sven, Wraith King, Phantom Assassin, Templar Assassin can have their damage mitigated by Cold Embrace.

* Heroes who rely on invisibility, such as Bounty Hunter, Clinkz, Mirana, Nyx Assassin and Riki, as they will be revealed if caught by Chronosphere.

* Melee heroes with low mobility can be kited and killed by Viper: Treant Protector, Kunkka, Alchemist, Troll Warlord, Wraith King, Tiny, Sven.

* Corrosive Skin minimizes the damage from Impale and Mind Flare.
* Nyx Assassin cannot survive several poison damage-over-time, even Spiked Carapace is activated.

* Heroes who can delivers a big chunk of damage in few hits will find themselves struggle against Templar Assassin's Refraction: Sven, Phantom Assassin, Ursa, Wraith King, Lifestealer

* Impale and Spiked Carapace stun can be instantly dispelled by Aphotic Shield.
* Abaddon can use Borrowed Time and easily heal for the duration of Borrowed Time by Nyx's burst damage.

* Nyx Assassin wants to start ganking as soon as he gets his Vendetta. Keeping him Tracked prevents him from ganking, and thus from doing his job in the game.
* Nyx Assassin has a lot of armor and health regen, making the nuke damage from Shuriken Toss very good against him.
Additional:
* Track hinders Nyx Assassin's ganking attempts with Vendetta, making him an easy kill for gold as well.

* Heroes who rely on physical damage are easily negated by Ghost Shroud: Phantom Assassin, Wraith King, Juggernaut.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.

* Some abilities deals damage from an independent source and not from the hero itself, so Nyx cannot counter them with Spiked Carapace: illusions or summoning units, Homing Missile, Nimbus, Mass Serpent Ward, Death Ward and especially Techies's mines.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.

* Melee heroes who may struggle to get close to Sniper: Wraith King, Kunkka, Doom, Tidehunter, Underlord, Troll Warlord, and etc.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

Additional:
* Duel's long duration prevents Nyx Assassin escaping from Vendetta. With Aghanim's Scepter, she can also bypass Spiked Carapace.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* Heroes with invisibility will be detected by Thirst when they have low enough health: Bounty Hunter, Templar Assassin, Riki, Clinkz, Weaver, Treant Protector, Nyx Assassin.

Additional:
* While Burrowing, Nyx is an easy target for a Blood Rite, although he can at least partially counter it with a well-timed Spiked Carapace.
* Thirst is always a threat to Nyx Assassin, hindering his attempt of escape using Vendetta.
* Rupture also prevents Nyx Assassin from escaping with Vendetta, as it forces him to stay still.

* Heroes who are reliant on physical damage will be nullified by Decrepify: Riki, Wraith King, Juggernaut.

* Heroes who rely on basic attacks will suffer from Laser: Phantom Assassin, Wraith King, Huskar.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.

* Heroes who build Black King Bar as either core or situational item will be able to fight back against Nyx Assassin and freely attack him as Spiked Carapace cannot pierce spell immunity at all: Axe, Broodmother, Dawnbreaker, Enigma, Huskar, Jakiro, Legion Commander, Lina, Luna, Lycan, Slardar, Slark, Troll Warlord, Witch Doctor.

* A well-timed Doom prevents Nyx Assassin escaping with Vendetta and fighting back with Spiked Carapace.
* Doom's high health also allows him to easily shrug off Nyx Assassin's burst damage and fend him off.

* Wraith King has no form of AoE to clear Terrorblade's illusions.
* Terrorblade is a common Manta Style and Diffusal Blade carrier.
* Terrorblade has very high armor, which helps against Wraith King's physical-only damage.
* A reincarnated Wraith King is an ideal target for Sunder if Terrorblade's health is low.
Additional:
* Terrorblade has very high armor gain, which helps him against Wraith King's physical damage.
* Wraith King is not good against illusion-based heroes as he has no AoE form abilities to deal with Terrorblade's Illusions.
* Terrorblade is a common Manta Style and Diffusal Blade carrier to help deal with Reincarnation before Wraith King has Aghanim's Shard.
* A Reincarnated Wraith King is a good setup for Sunder if Terrorblade's health is low enough.

* A hero that Rubick cannot reliably kill in most cases, Wraith King is deceptively vulnerable to Rubick in teamfights.
* Rubick can kite Wraith King by casting Telekinesis should Rubick stays alive after first wave of skirmishes.
* {{A:Fade Bolt|Rubick} negates damage from Wraith King's skeletons.
* Wraithfire Blast is a spell very easy to stolen even for new Rubick players if Wraith King is on the other side.
* A 2 second stun with a 8 second cooldown (6 second with Rubick's Level 15 talent -25% Stolen Spells Cooldown, as of 7.31c) is already far enough to lockdown Wraith King to a crawl, as he does not have much mobility on his own and can be easily targeted.
* Reincarnation may sound insurmountable, but the extra 3 second delay already grant about half the cooldown duration for a stolen Wraithfire Blast.
* Rubick has sufficient mana pool to cast Wraithfire Blast multiple times.
* Although not the best option, Vampiric Spirit can be casted after Rubick gained enough last hits to summon skeletons for pushing and farming.

* Heroes which rely exclusively on right clicks will struggle somewhat against Blinding Light: Phantom Assassin, Wraith King, Medusa

* Invoker can drain Wraith King's mana with E.M.P., preventing him from reincarnating unless Wraith King has his Aghanim's Shard.
* Even if Wraith King survives and reincarnates, Invoker still has an arsenal of spells to lockdown Wraith King, including an easily setup Ice Wall.
* Tornado applies an area dispel to clear skeletons.
Additional:
* E.M.P. allows Invoker to burn Wraith King's mana to prevent Reincarnation from triggering (only until Wraith King gets his Aghanim's Shard).
* Ice Wall and Cold Snap are particularly crippling for Wraith King as they allow to kite him very effectively, preventing him from dealing melee attack damage.

* Weaver can run away after killing Wraith King once thanks to Shukuchi.
* Wraithfire Blast is quite predictable. If Weaver is quick, he will disjoint it with Shukuchi and proceed to chase Wraith King down.
* Shukuchi does have a fade time. They cannot disjoint it if you use it right next to them. They will be stunned and take damage; however they will still become invisible if they used Shukuchi before the stun hits.
* Weaver can easily harass Wraith King out of his lane thanks to his high base damage and Geminate Attack.
* Weaver can burn Wraith King's mana quickly with his Mana Break or Diffusal Blade, until Wraith King purchases Aghanim's Shard to remove Reincarnation's manacost.
Additional:
* Wraithfire Blast is easy to disjoint with Shukuchi or Time Lapse, and it's the only way to break Weaver's Linken Sphere.
* Wraith King has no other disables and no mobility, allowing Weaver to chase or escape Wraith King as he wishes.
* With the Mana Break talent and Diffusal Blade, Weaver can prevent Reincarnation from triggering until Wraith King gets his shard.

* Wraith King, Medusa, Storm Spirit and other mana dependent heroes will have diminished impact on a fight if they survive Fiend's Grip due to its mana steal.

* Sanity's Eclipse does massive damage to Wraith King who naturally has a low mana pool and typically doesn't build items to increase it.
* Wraithfire Blast's slow projectile speed makes it easy to avoid using Astral Imprisonment.

* Heroes who rely on damage over time as Spiked Carapace can block and reflect only one instance of damage: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom, Dawnbreaker. However, this also means they are easily stunned.