* His Poison Attack is very useful against Huskar, since he tends to stay at low health.
* Nethertoxin disables passive skills like Berserker's Blood.
* It is dangerous for Huskar to jump on Viper because Corrosive Skin and Viper Strike with the slowdown of movement and attack speed which usually will be deadly for Huskar.
Additional:
* Nethertoxin disables Berserker's Blood, which Huskar relies upon for attack speed and healing.
* The damage from Burning Spear and Life Break is largely absorbed by Corrosive Skin. It also will return some damage, making it risky to use Burning Spears in the laning stage.
* Because Huskar wants to be on low health for Berserker's Blood, he is particularly vulnerable to Poison Attack.

* He's the kind of hero that likes to remain at low hp, which is perfect for Queen of Pain to burst with Sonic Wave.
* You should be able to blink away after he jumps on you with Life Break.

* Queen of Pain can Blink to both escape and initiate onto Void Spirit.
* She is also a very common Orchid Malevolence carrier, which can prevent Void Spirit from contributing much in fights.

* Poison Attack makes it hard for Void Spirit to lane against him.
* Corrosive Skin reduces the magical damage from Void Spirit's spells.

* Viper's Poison Attack and Viper Strike that can slow Razor, and is one of the few heroes that can keep him immobile.
* Altogether, Viper's skills reduce Razor's attack speed, heavily reducing the benefit of the damage drain from Static Link.
Additional:
* Storm Surge is counteracted by Nethertoxin, leaving Razor without faster MS.
* Static Link's damage drain doesn't bother Viper a lot as most of his early to mid game damage is magical.

* Blink can instantly break Static Link, making it useless against her.
* Queen of Pain doesn't fully rely on her physical attack damage, so she can still fight after being hit with Static Link.

* Blink allows Queen of Pain to avoid ganks and keep her distance, preventing Monkey King from building up Jingu Mastery.
* Scream of Pain and Sonic Wave will hit Monkey King when he is disguised, or on a tree.
* The large AoE and low cooldown also helps Queen of Pain hit the real Monkey King inside of Wukong's Command.

* Nethertoxin prevents the buildup of Jingu Mastery stacks.
* Viper's poison magical damage-over-time stops Monkey King from using Tree Dance. It also ignores the extra armor bestowed by Wukong's Command.
Additional:
* Nethertoxin prevents the buildup of Jingu Mastery stacks.
* Monkey King's high base movement speed is of little worth against the array of slows Viper possesses.
* All of Viper's magical damage over time stops Monkey King from using Tree Dance. It also ignores the extra armor bestowed by Wukong's Command.

* Nethertoxin breaks both Necromastery and Presence of the Dark Lord, reducing his damage massively.
* Corrosive Skin gives Viper bonus Magic Resistance against Shadowraze and Requiem of Souls.
* Viper can easily take advantage of Shadow Fiend's lack of escape and mobility spells with Viper Strike and Poison Attack. Poison Attack also serves as a great way to harass Shadow Fiend.

* Heroes with high burst damage: Lina, Lion, Luna, Nyx Assassin, Queen of Pain.

* Nethertoxin disables Vengeance Aura.
* Vengeful Spirit has no mobility spells aside from Nether Swap, which Viper can take advantage of with his slows.
* Viper can easily bully Vengeful Spirit out of a lane with Poison Attack.
Additional:
* Nethertoxin prevents attack damage bonus from Vengeance Aura and the components of Nether Swap.
* Both Magic Missile and Wave of Terror are counteracted by Corrosive Skin, making Vengeful Spirit's fighting harder against Viper.

* Heroes who have a high mobility (Queen of Pain, Storm Spirit, Slark, etc.).

* Nethertoxin breaks Sniper's passives.
* Viper Strike together with Poison Attack can slow Sniper and tears through his low health and mobility.

* Heroes with high mobility can approach Sniper: Anti-Mage, Earth Spirit, Io, Nature's Prophet, Pangolier, Puck, Queen of Pain and most notably Riki.

* The damage over time from Viper's Poison Attack and Viper Strike rapidly wear down Refraction charges, allowing Templar Assassin to be damaged. Additionally, Corrosive Skin causes her attacks to apply damage over time on her as well.
* Nethertoxin is a big threat to Templar Assassin. Her initially low range making it very hard to deal against Nethertoxin in laning phase. At any stage of the game, a Nethertoxin can always force her to undo her Meld.
Additional:
* All of Viper's abilities quickly burn through Refraction charges.
* Templar Assassin's short range, aside from Psi Blades' spill damage, makes her vulnerable to Poison Attack harassment.
* Templar Assassin traditionally forgoes health and armor items for damage. Outside of Black King Bar, Viper will almost always be able to kill her when Refraction is down.

* Weak damage but high tick rate or persist in a long time: Slark, Gyrocopter, Queen of Pain, Shadow Shaman (Shackles), Pugna
* Heroes that can quickly deal damage to her, regardless of how weak they are, can easily break through her Refraction:
* Multiple attackers thanks to summoned units or clones: Meepo, Witch Doctor, Lycan, Enigma, Shadow Shaman
* Multiple attackers thanks to illusions: Phantom Lancer, Chaos Knight, Naga Siren (bonus for her Ensnare). Also despite the visual effects, Templar Assassin does not spill damage against illusions or buildings, so she is not a really good hero to clean up illusions.
* Weak damage but high tick rate or persist in a long time: Slark, Gyrocopter, Queen of Pain, Shadow Shaman (Shackles), Pugna

* Nethertoxin prevents Timbersaw from gaining stacks on Reactive Armor with silence talent also prevents Timbersaw using his abilities.

* Timbersaw has a difficult time against magical and pure damage: Lina, Leshrac, Enchantress, Queen of Pain

* Heroes with damage over time abilities can quickly eat through Gravekeeper's Cloak charges like Huskar, Jakiro and Queen of Pain.

* Nethertoxin cuts off Gravekeeper's Cloak, Visage's primary defense mechanism.
* Viper can ignore Grave Chill's attack speed slow with his magic damage output.
Additional:
* Since Visage is a slow hero, Viper can easily kite him with Poison Attack and Viper Strike while successfully chipping away at Gravekeeper's Cloak.
* Nethertoxin removes all layers of Gravekeeper's Cloak, leaving Visage exposed.
* Corrosive Skin makes Viper highly resistant to Soul Assumption.

* Corrosive Skin minimizes the damage Viper takes from all of Ancient Apparition's abilities.
* Ancient Apparition's slow movement speed, squishy nature, and lack of escape abilities can easily be taken advantage of through Poison Attack and Viper Strike.

* Heroes with mobility/escape mechanisms to dodge Ancient Apparition abilites, or to easily jump on him: Riki, Queen of Pain, Phantom Assassin, Windranger, Bounty Hunter, Spirit Breaker, Night Stalker, Storm Spirit, Juggernaut, etc.

* Both Scream of Pain and Sonic Wave should hit him during his Shadow Dance.

* Nethertoxin negates Essence Shift and the regeneration aspect of Shadow Dance.
* Dark Pact doesn't mean a lot against Viper's ubiquitous slows.
* Viper becomes a relevant presence in team fights before Slark can procure his standard items (e.g. Shadow Blade).

* Heroes with break can disable Untouchable for a while: Doom and Shadow Demon (via Aghanim's Scepter), Viper

* Heroes that can jump on her: Slark, Queen of Pain, Anti-Mage

Additional:
* Untouchable won't mitigate magic damage, and a squishy Enchantress is very vulnerable to Queen of Pain's magic burst.

* The slow applied from Corrosive Skin offsets the movement speed bonus granted by Scorched Earth and the tick-based damage from Infernal Blade and Doom will continually slow Doom down. This allows Viper, much like Sniper, to 'kite' Doom and keep him at a safe distance between the two. Additionally, Corrosive Skin applies an attack-speed slow which is fairly crippling to a hero such as Doom that, naturally, has a high base attack-time, poor agility gain and builds little attack-speed items.
* Since Doom does not disable auto-cast abilities, Viper's Poison Attack will continue to work. Doom may find it hard to close the distance between himself and Viper, and thusly difficult to effectively lockdown and continually deal damage through his abilities.

* Tiny has low movespeed and attack speed, making him vulnerable to Viper's slows.
* Corrosive Skin provides magic resistance to lower Tiny's magic burst damage.

* Nethertoxin disables Bristleback's passive.
* Viper Strike and Poison Attack slow down Bristleback's movement speed so he's unable to get out from Nethertoxin.
Additional:
* Nethertoxin's break removes Bristleback and prevents Warpath from building stacks. Besides losing his eponymous defensive passive, Bristleback also lose his ability to build up damage over lengthy battles.
* Viper can perpetually kite Bristleback with Poison Attack and Viper Strike.

* Most of Magnus' abilities except Empower will trigger damage through Corrosive Skin.
* Poison Attack and Viper Strike can slow Magnus during Skewer, as well as putting his Blink Dagger on cooldown, preventing him from initiating or re-initiating.

* Nethertoxin disables Desolate and Dispersion, leaving Spectre with far less damage output and damage mitigation in engagements.
* Spectre is one of the weakest heroes at early levels. Viper can stifle her farm with early fights before Spectre purchases any major items.
Additional:
* Nethertoxin removes passives, negating Spectre's damage and survivability by removing both Dispersion and Desolate.
* Due to Haunt and Radiance's burn, Spectre is heavily susceptible to being persistently slowed and damaged by Corrosive Skin without even directly attacking Viper.
* Poison Attack and Viper Strike further slow Spectre's movement speed to a crawl, while his improved magic resistance means he can easily shrug off Radiance's burn.

* All of Queen of Pain's abilities are active, making Demonic Purge break from Aghanim's Scepter useless.
* Although, Demonic Purge can help his allies kill a squishy Queen of Pain.
* Blink allows Queen of Pain to escape from Shadow Demon's abilities if he doesn't have disables.
* An attempt to save an ally using Disruption can easily become a perfect setup for a Sonic Wave for the enemy.
* Queen of Pain usually builds Eul's Scepter of Divinity to dispel Shadow Poison and Soul Catcher and Linken's Sphere or Spell Block talent to block Disruption and Demonic Purge.

* Nethertoxin prevents buildup of Fiery Soul stacks.
* Corrosive Skin provides magic resistance against Lina's spells.
* Poison Attack and Viper Strike can burn away Lina's small health pool.

* Blink makes it hard for Gyrocopter to pin down Queen of Pain.
* Sonic Wave is very effective at ganking Gyrocopter in the early game.

* Nethertoxin breaks the damage block from Bulwark.
* Poison Attack and Viper Strike's slows make it difficult for Mars to contribute to fights due to his low mobility.
Additional:
* Nethertoxin breaks Bulwark entirely, making Mars far less tanky. Using Nethertoxin inside Arena of Blood may discourage enemies from following up with Mars' initiation.
* Rod of Atos is currently common on Viper and keeps Mars in position long enough to be killed.
* Viper is not very tanky earlier in the game, so positioning against Mars is important since a well-timed Spear of Mars can be the end of Viper.

* Poison Attack and Viper Strike allowing to kite and slow Earthshaker significally, putting Blink Dagger on cooldown and preventing him from initiating or re-initiating.
* Nethertoxin breaks Aftershock. The silence from Level 25 talent also prevents Earthshaker from initiating or re-initiating.
Additional:
* Being a melee hero, Earthshaker's movement is liable to suppression by Poison Attack and Viper Strike.
* Earthshaker's kit, with the exception of Enchant Totem, deals magic damage. Corrosive Skin effectively blunts his killing potential with a standard Blink combo among other things.
* Nethertoxin disables Aftershock, which removes the stun and bonus damage from Enchant Totem and Echo Slam. Additionally the level 25 talent will silence Earthshaker, making him vulnerable to Viper's teammates without stuns.

* Corrosive Skin counters Zeus in lane by canceling the effects of Clarity as Zeus relies on Arc Lightning to farm and secure last hits.
* Corrosive Skin also increases Viper's magic resistance to shrug off Zeus's magical nukes.
* Nethertoxin breaks Static Field.
* Due to Zeus' poor mobility, Viper Strike will cripple Zeus and will allow Viper and his teammates to land a lot of attacks.
Additional:
* Corrosive Skin severely reduces Zeus's damage output throughout the game.
* During the laning stage, Viper can abuse Zeus' reliance on spells by hugging the creep wave. Zeus will take constant damage over time from Corrosive Skin unless he drives Viper from the lane or returns to farming in his absence.
* Prior to buying Blink Dagger or Force Staff, Zeus is fragile and possesses low mobility. Any of Viper's numerous slows can set up an easy kill.

* 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.

* Often you can burst Drow Ranger down before she has a chance to try and Gust you away. Try to have a teammate bait her Gust out before you Blink and get the drop on her.

* In the early game, a Dragon Knight without Black King Bar is basically defenseless against Viper.
Additional:
* Dragon Knight is easily harassed by Poison Attack after the laning stage ends.
* Corrosive Skin protects Viper from Breathe Fire and returns damage.
* Nethertoxin mitigates Dragon Blood, Dragon's Knight main source of armor and health regeneration.
* Between Poison Attack and Viper Strike, Viper can keep Dragon Knight permanently slowed even in Elder Dragon Form.

* Blink allows Quen of Pain to easily escape ganking or initiating attempts with Hookshot and Power Cogs.

* Nethertoxin breaks Fury Swipes, making Viper a decent counter to Ursa in a laning stage.
* Viper Strike is a strong, undispellable slow, making it much easier to kite Ursa for everyone.

* Corrosive Skin makes Viper receive less damage from Invoker's spells
* Viper can harass Invoker with his Poison Attack in the early game.
* Viper Strike and Poison Attack can kill Invoker easily if Ghost Walk is on cooldown.

* Queen of Pain usually outlanes Invoker, giving her team a significant early game advantage while Invoker is still farming.
* Blink allows Queen of Pain to escape from Invoker's combo if he doesn't have disables.

* Corrosive Skin means Viper can often outlast Venomancer in a battle of attrition.
* Venomancer has no mobility without items, which makes him vulnerable to constant slows.

* Corrosive Skin gives Viper additional resistance to Phoenix's magical damage, and since they deal damage over time, Phoenix would be constantly afflicted by his passive's own debuff, making him not an ideal target for Phoenix's harassment. Phoenix's abilities also constantly drain its own health away, becoming more vulnerable to Poison Attack.

* Viper's poison abilities can slow Bounty Hunter's movement speed and allows to chase him with True Sight items.
* Nethertoxin can break Jinada, and the silence from level 25 prevents Bounty Hunter from using all of his spells.

* Nethertoxin cancels out Kraken Shell and stops the hard dispel from passively activating, preventing Tidehunter from functioning as a frontline tank.
* Anchor Smash is mostly irrelevant against a ranged hero.
* Tidehunter relies on the threat of Ravage, which has an obscenely long cooldown. Viper can exploit the downtime with his short cooldowns.

* Because Poison Attack has a low cooldown at all levels, Aphotic Shield is ineffective as a hard dispel.
* Nethertoxin prevents Borrowed Time from activating passively and blocks Curse of Avernus

* Nethertoxin breaks Multicast.
* Corrosive Skin minimizes the damage during Ignite and Fireblast.

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

* Heroes with teleports to escape Will-O-Wisp: Phantom Assassin, Puck, Queen of Pain, Storm Spirit

* Heroes with mobility spells (such as Queen of Pain's Blink and Clockwerk with Hookshot) can easily avoid Lil' Shredder and Mortimer Kisses.
* Heroes with high movement speeds like Pugna and Meepo can run around, to, or away from Snapfire during Mortimer Kisses and dodge the projectiles easily due to their slow speed.

* Queen of Pain can be a good hero for dealing with Ember Spirit with Orchid Malevolence, her pure damage nuke in Sonic Wave and a slow in Shadow Strike. However, Queen of Pain can be punished by Ember Spirit, as his Searing Chains prevents her from getting Blink off.

* Heroes with a high degree of mobility and invisibility are hard to catch with Meat Hook: Ember Spirit, Riki, Clinkz, Queen of Pain.

* Heroes with mobility spells can quickly escape from Stroke of Fate or break out of Soulbind: Anti-Mage, Queen of Pain, Morphling, Storm Spirit

* Blinking heroes like Anti-Mage or Queen of Pain can often chase down an injured Brewmaster after his ultimate expires.

* Heroes who can harass Omniknight out of lane will keep him weak in the mid game: Viper, Venomancer, Clinkz

* Hand of God has a long cooldown, so damage over time spells can be hazardous for Chen, forcing him to use it prematurely: Jakiro, Venomancer, Viper, Dazzle, Phoenix.

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

* Heroes with considerable mobility can easily escape from a rolling Pangolier: Anti-Mage, Queen of Pain, Void Spirit, Storm Spirit, Ember Spirit, Earth Spirit, moreover, if a player is familiar with how Rolling Thunder work, they can adjust their movement to avoid it entirely and of course outplay the Pangolier player.

* Heroes that can slow Charge of Darkness by a huge amount: Venomancer, Viper, Dazzle, Arc Warden

* Heroes that usually builds Linken's Sphere as a core item: Weaver, Medusa, Morphling, Queen of Pain, Storm Spirit

* Heroes that have superior mobility that can easily catch up with Mirana even after she used Leap to escape: Anti-Mage, Queen of Pain, Storm Spirit, Riki.

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

* Heroes with escaping and disjointing abilities can be good against Juggernaut: Riki, Queen of Pain, Puck, Storm Spirit, Ember Spirit, Slark etc.

* Viper can bully Alchemist out of mid lane quite easily, forcing him to either retreat into jungle, or stay harassed in lane, and get very few last hits. Vipers break also completely disables Greevil's greed which prevents Alchemist to earn his amazing amounts of money.

* Nethertoxin breaks Phantom Assassin's passive skills.
* Viper Strike goes through Black King Bar.

* Poison Attack and Viper Strike slows Axe significantly, and puts his Blink Dagger on cooldown, preventing him from initiating.
* Nethertoxin can break Counter Helix.
Additional:
* Nethertoxin prevents Counter Helix from triggering, which significantly lowers Axe's damage output in the early to mid game.
* Viper's various slows and damage over time prevents Axe from initiating as well as putting his Blink Dagger on cooldown.

* Nethertoxin prevents Heartstopper Aura from dealing damage or healing Necrophos.
* Viper's magic damage is amplified whenever Ghost Shroud is used.
* Corrosive Skin makes Viper tankier against Death Pulse and Reaper's Scythe.

* Nethertoxin prevents the lifesteal from Ransack. The silence from Viper's level 25 talent also prevents Meepo escaping with Poof.
* Meepo and his clones have a lack of magic resistance, so they're vulnerable to Poison Attack & Viper Strike directed onto one clone.

* Corrosive Skin minimizes the damage Viper takes from all of Disruptor's skills.

* Heroes with damage-increasing passive abilities, such as Viper and Riki, will usually kill Silencer in a short time before he even has time to set up his abilities.

* Heroes who can easily harass Crystal Maiden out of lane in the early game (Clinkz, Viper) can prevent Crystal Maiden from being able to level effectively, and can ultimately slow down her level 6, 12, and 18 to a point where enemy carries already have items to address her ultimate.

* 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.

* Once you farm up an Orchid Malevolence or a Scythe of Vyse, you're suddenly a lot more fearsome to elusive heroes like Storm Spirit or even that pesky Puck.

* Viper's Nethertoxin disables Cloak and Dagger, negating Riki's invisibility and much of his damage. It also makes him more vulnerable to magic damage, which does not go well with Riki's low health pool. With the talent applied, he can't even blink to safety or hide with Tricks of the Trade.
* Corrosive Skin makes it hard for Riki to chase Viper and attack him due to the attack speed slow.
* Viper Strike stays on Riki even after he goes invisible.
* Poison Attack makes it risky for Riki to get last hits and can make the laning phase difficult for him.

* Corrosive Skin minimizes the damage from Impale and Mana Burn.
* Nyx Assassin cannot survive several poison damage-over-time, even Spiked Carapace is activated.
* However the Vendetta break can be dangerous for Viper.