* Anti-Mage commonly builds Battle Fury, which can deal with Phantasm illusions easily.
* Counterspell, if timed right, will turn Chaos Bolt against the Knight, and can set up for a kill if he is not careful.
* Even if Counterspell is on cooldown, Blink can almost always dodge a Chaos Bolt because of its slow projectile.
* Mana Break will quickly drain Chaos Knight's mana.

* Dark Seer's strength lies in his high-mana cost skills. So Mana Break can be a great nuisance for him, since it can reduce his mana and prevent him from casting his spells.
* Mana Void can deal a lot of damage if Dark Seer spent a lot of mana on his abilities.

* Ember Spirit is evasive and can dodge close encounters with melee heroes like Chaos Knight. Ember Spirit can't be caught with the slow from Reality Rift, and Flame Guard and Sleight of Fist can bring Phantasm's illusions down quickly.

* Flame Guard makes Dark Seer not deal any damage with his skills to Ember Spirit.

* Tidebringer, Torrent and Ghostship destroys Chaos Knight's Phantasm army all through the game.

* X Marks the Spot prevents Dark Seer or his allies from escaping with Surge.

* In general, heroes who are melee with no way to fight back can be very easily poked by Monkey King to gain his Jingu Mastery stacks: Dark Seer, Riki, Rubick.

* Wukong's Command and Boundless Strike combo can easily cause havoc on Chaos Knight by destroying all of his powerful illusions.
* Chaos Knight without Phantasm cannot deal with Jingu Mastery at all.

* The area of effect damage from Midnight Pulse and Black Hole help deal with Chaos Knight's illusions.
Additional:
* Black Hole usually catches Chaos Knight with all his illusions.
* Midnight Pulse deals damage based on max health, quickly killing Phantasm illusions.

* Decrepify turns the target ethereal, protecting them from Chaos Knight's and his illusions' attacks.
* Life Drain instantly destroys illusions. It can effectively negate Phantasm when upgraded with Aghanim's Scepter.
* Nether Blast quickly clears out illusions and can harass Chaos Knight in lane.

* Puck's area of effect nukes in the form of Illusory Orb and Waning Rift clears Phantasm illusions from the early game to mid game.
* Phase Shift can be used to disjoint Chaos Bolt.

* Abaddon could punish Chaos Knight for using his Phantasm and Reality Rift combo on him with Aphotic Shield. Additionally, it provides extra protection against Chaos Knight's potential to take Abaddon down quickly.
* Furthermore, Abaddon's Borrowed Time makes it utterly impossible to burst Abaddon down, effectively reducing the amount of targets Chaos Knight can threaten by 1 for the entire game.

* Fortune's End can dispel Ion Shell, which cripples Dark Seer economy since it's his most efficient tool for farming.
* Fortune's End can dispel Surge, effectively slowing his movement speed making him vulnerable to ganks or skirmishes.
Additional:
* Fortune's End dispels Ion Shell and Surge, making any gank attempt on Dark Seer in the laning phase likely to succeed.
* Fate's Edict prevents all magical damage that comes from Dark Seer's abilities.
* Fortune's End dispels Ion Shell on creeps, which Dark Seer relies on to farm and zone.

* With his AoE damage, Jakiro can easily kill Chaos Knight's Phantasm illusions.
* Chaos Knight usually doesn't buy a Black King Bar, making him vulnerable to an Ice Path into Macropyre combination.
Additional:
* Ice Path and Macropyre punish Reality Rift with a long stun and heavy damage across all illusions.

* Flak Cannon destroys Chaos Knight's illusions very quickly.

* Ravage damages and disables Chaos Knight's army.
* Anchor Smash deals respectable area damage at early levels and lowers Chaos Knight's damage.
* Kraken Shell dispels Chaos Bolt and Reality Rift while providing protection from damage.

* Storm's Dispel Magic combined with Thunder Clap deals high damage against Chaos Knight's illusions even in the late game.
* Chaos Knight's reliance on physical damage is easily hindered by Drunken Brawler.
* Chaos Knight's lack of area effect and mobility makes him easily overwhelmed by Primal Split.
Additional:
* Dispel Magic from {U:Storm} can instantly kill the Phantasm army early on, and can still deal a lot of damage to them late game, revealing the real Chaos Knight.

* Cold Embrace protects targets of Reality Rift.
* Winter's Curse turns Phantasm illusions against Chaos Knight or a teammate.
* Splinter Blast deals decent area damage to Phantasm illusions.
* Arctic Burn's percentage-based damage quickly wears down Chaos Knight's health.
Additional:
* Winter Wyvern can make Chaos Knight's illusions attack the real one, provided the player knows who it is.
* Alternatively, Winter's Curse can make Chaos Knight and all his illusions attack one of his allies.
* Cold Embrace protects ally who is focused by Chaos Knight.
* Splinter Blast deals decent area damage to Chaos Knight's illusions.

* A Sniper who is somewhat competent at positioning is hardly going to be affected by any of Dark Seer's spells thanks to Take Aim.
* However, an illusion of Sniper made with Wall of Replica is extremely powerful, and hard to deal with.

* Echo Slam's damage potential increases due to Chaos Knight's Phantasm illusions.
Additional:
* Echo Slam will deal a colossal amount of damage to your army, as will Fissure at lower levels.
* The area stuns from Aftershock will always slow down your illusions, since they can't have spell immunity.

* Reactive Armor helps Timbersaw to endure the damage from Chaos Bolt and Reality Rift combo.
* Timbersaw's large amount of pure damage AoE nukes clears Chaos Knight's illusions quickly, drastically reducing his damage.
Additional:
* Strong area damage, particularly from Whirling Death and Chakram, lets Timbersaw clear out illusions quickly.
* Whirling Death directly reduces Strength from both Chaos Knight and his Phantasm illusions, reducing both the damage output and raw health that the hero relies on.
* Reactive Armor quickly builds stacks against Phantasm illusions, making Timbersaw hard to kill.
* Timber Chain allows Timbersaw to escape while surrounded.

* Dragon Blood's armor bonus greatly reduces the damage dealt by Phantasm.
* Breathe Fire and Elder Dragon Form's splash damage quickly destroy illusions and reduces their damage output.

* Berserker's Call and Counter Helix makes short work of Chaos Knight's Phantasms.
Additional:
* Berserker's Call allows Axe to lock down Chaos Knight and his illusions.
* Counter Helix combined with Blade Mail clears illusions out in no time.

* Phantasms can be easily killed with Purification.
* Heavenly Grace dispels the stun from Chaos Bolt and the armor reduction from Reality Rift.
* Guardian Angel works well against Chaos Knight's overwhelming reliance on physical burst damage.
Additional:
* Purification heals a teammate targeted by Reality Rift and heavily damages Chaos Knight and his illusions in the process.
* Guardian Angel blocks all of Chaos Knight's damage for a duration.

* Maledict cannot be dispelled by Phantasm, and can be used to tag the real Chaos Knight hiding within his illusions.
* If Witch Doctor has an Aghanim's Scepter, Death Ward will bounce between Chaos Knight's illusions, destroying them quickly.
* However, Death Ward is easily interrupted by Chaos Bolt until Witch Doctor buys Glimmer Cape or Black King Bar.

* Quill Spray quickly destroys Chaos Knight's Phantasms.

* Using Reality Rift sets up a Reverse Polarity on Chaos Knight and his illusions.
* Shockwave and Skewer kill Phantasm's illusions quickly, as can Empower cast on a melee carry.
Additional:
* All Magnus abilities are very good against Chaos Knight's Phantasm illusions.

* Great Cleave is very effective against Chaos Knight's illusions.
* Storm Hammer's radius can catch all of Chaos Knight's illusions at once, especially after Reality Rift.
* Warcry shields Sven and his teammates against Chaos Knight's burst physical damage.
Additional:
* Storm Hammer's faster projectile speed and cast time allows Sven to stun Chaos Knight and his illusions before he can cast Chaos Bolt.
* Warcry's armor bonus counteracts Reality Rift's debuff and reduces Chaos Knight's damage output.
* Great Cleave and God's Strength devastates Phantasm illusions.

* Deals damage over time: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom
* The nature of some abilities turn them into an easy target for a turnover from Spiked Carapace:
* Slow-moving projectiles: Skywrath Mage, Tinker, Necrophos
* Large area-of-effect with delay or require channeling: Enigma, Crystal Maiden, Invoker, Shadow Fiend, Pugna, Keeper of the Light
* Deals damage over time: Venomancer, Huskar, Ember Spirit, Dark Seer, Sand King, Doom

* Illusion based heroes (like Chaos Knight and Terrorblade) can't use their illusion beneficially against Sanity's Eclipse's high AoE burst damage.

* In general, melee heroes without blink mechanisms or spell immunity will have a hard time positioning against Pit of Malice: Sven, Tiny, Wraith King, Dragon Knight, Meepo, Doom, Bounty Hunter, Dark Seer, Undying, Alchemist, Legion Commander.

* Because of his massive AoE damage, Sand King is very effective against illusion heroes: Chaos Knight, Phantom Lancer, Terrorblade,...

Additional:
* Sand King's massive area damage output, particularly Epicenter, allows him to quickly take down Chaos Knight and his illusions.
* He can apply Caustic Finale to illusions with attacks for extra damage.

* As long as Windranger is able to identify the real hero among the illusions, heroes relying on them can be easily tagged with Focus Fire: Chaos Knight, Terrorblade, Phantom Lancer, Naga Siren.

* A well-timed use of The Swarm provides vision over heroes with high mobility: Anti-Mage, Arc Warden, Dark Seer.

* One of Lion's level 20 talents lets Mana Drain affect 2 secondary targets. This can make things difficult for heroes like Phantom Lancer, Chaos Knight, and Terrorblade who rely on illusion armies.
* Mana Drain and Hex instantly kill any illusions. Finger of Death upgraded with Aghanim's Scepter also shreds most illusions.
* One of Lion's level 20 talents lets Mana Drain affect 2 secondary targets. This can make things difficult for heroes like Phantom Lancer, Chaos Knight, and Terrorblade who rely on illusion armies.

Additional:
* Mana Drain is a real problem to Chaos Knight in the early game, considering his already low mana pool.
* Aghanim's Scepter upgraded Finger of Death is an AoE ability, which can deal a tremendous amount of damage to his illusions.
* Lion has two abilities that can instantly kill illusions. Provided that he does not get stunned by Chaos Bolt first, Lion can render Phantasm near-useless.

* Illusion-based heroes such as Naga Siren or Chaos Knight are vulnerable to Phoenix's DPS and attack speed slow, as their illusions, no matter how many, will be unable to deal enough damage to actually be a threat, and they will all be completely useless against the Supernova.

* Heroes who are reliant on illusions: Chaos Knight, Phantom Lancer, Naga Siren.

* Heroes who rely on illusions will see them destroyed easily by Overwhelming Odds: Phantom Lancer, Chaos Knight, Terrorblade, Naga Siren

* Heroes who are reliant on illusions or summons: Chaos Knight, Broodmother, Naga Siren.

* Dark Seer's only disable is Vacuum. Though he starts off with high armor and health, he'll eventually have a hard time dealing with high mobility heroes such as Weaver or Queen of Pain.

* Heroes reliant on illusions or summons: Broodmother, Chaos Knight, Naga Siren.

* Melee carries will have a hard time against Tiny's Craggy Exterior: Phantom Assassin, Chaos Knight, Juggernaut.

* With Aghanim's Scepter, Tinker's Laser completely stops Chaos Knight's damage, forcing him to buy either a Black King Bar for his own survivability while leaving his illusions still vulnerable, or a Monkey King Bar leaving him still vulnerable to Tinker's nukes, though improving his damage.
* Tinker rarely finds himself in the middle of a fight, which is where Chaos Knight typically thrives, and even in the rare cases of being so, at level 3 Tinker's constant rearm and blink away can kite and dodge Chaos Knight's spells reliably, so Chaos Knight has very little catch against Tinker's mobility. This gives Tinker impunity to create more chaos in a teamfight than Chaos Knight can control, laying down the field with March of the Machines and constantly being hit by rockets and lasers.
Additional:
* Tinker's Aghanim's Scepter upgraded Laser can blind him and all of his Phantasm illusions.

* Chaos Knight's single target abilities are difficult to target against Phantom Lancer's illusions.
* Chaos Knight's lack of mobility makes him an easy target for Phantom Lancer to Phantom Rush and drain his already low mana pool.
Additional:
* Juxtapose allows Phantom Lancer to overwhelm Chaos Knight due to his single-target abilities.
* Doppelganger can be used to dodge Chaos Bolt.
* Spirit Lance can be used to harass Chaos Knight during the early game.
* Since Phantom Lancer builds Diffusal Blade often, it can quickly drain Chaos Knight of all his mana, leaving him unable to cast spells.

* 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.
Additional:
* 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.

* The constant dispel from Demonic Purge will make any attempt to save the victim or himself by Surge become futile. For what it's worth, Demonic Purge will also dispel Ion Shell.