* 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.

* Whirling Death deals damage as well while reducing 15% of Bristleback's strength, which reduces Bristleback's tankiness.
* Reactive Armor can sustain through multiple Viscous Nasal Goo and Quill Spray stacks.
* Timber Chain makes it hard for Bristleback to slow down Timbersaw with Viscous Nasal Goo.

* 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.

* Because multiple Meepos tend to clump up, they present an easy target for Timbersaw's many area abilities.

* Timbersaw's pure damage will kill Dragon Knight surprisingly fast, especially if he gets caught in a bad position while laning.

* 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.

* Whirling Death reduces Axe's strength by 15%, making him much less tanky, especially in the early game. It is also stackable.
* Axe's Blade Mail is ineffective against attribute changes, and Timbersaw's mobility with Timber Chain means he can wait out Blade Mail's duration.
* Reactive Armor's armor and regeneration makes it much harder for Axe to finish Timbersaw with Culling Blade.
* Chakram disarms Timbersaw, making Counter Helix less effective.

* 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.

* Razor deals mostly physical damage towards the later game, and Timbersaw is also very mobile, making him a difficult kill to earn.
* Timbersaw rarely resorts to attacks, thus does not suffer when his damage is stolen with Static Link.

* 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.

* 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.

* Reactive Armor will quickly stack up from Familiar attacks, making Timbersaw hard to kill.
* Visage's low mobility makes it easy for Timbersaw to line up his abilities.

* With Timber Chain, Timbersaw can slow, catch up with, or escape from Chen and his creeps.
* Chakram can clear Chen's creeps and slow him.
* Attacks from multiple creeps quickly build Reactive Armor stacks.

* 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.

* 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.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

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

* Timber Chain can kite Troll Warlord extremely effectively.
* Whirling Death and Chakram deals lots of damage to Troll Warlord.
* Reactive Armor makes Timbersaw extremely resilient to Troll's attack damage and extreme attack speed, especially during Battle Trance.

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

* Not only are all of Timbersaw's active abilities capable of cutting down trees, but Whirling Death and Timber Chain also require it to be effective, counteracting both Treant Protector's Nature's Guise and Eyes in the Forest abilities.
Additional:
* Timbersaw can use his plethora of tree cutting abilities to level entire sections of the forest, making hiding in the trees more difficult for Treant Protector and his team.
* Timbersaw can easily cut down Treant Protector's Eyes In The Forest once his team has detection. He may even do it unknowingly due to the sheer destructive and chaotic nature of his abilities.

* 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).

* Timbersaw can use Chakram as a scouting tool to find Slark if he tries to Pounce into the trees.
* None of Timbersaw's abilities require a target to be cast, allowing him to hit Slark inside Shadow Dance.
* Reactive Armor can be effective protection against a Slark who attacks quickly, since the strong armor and health regen cannot be stolen by Essence Shift.
* Timber Chain makes Timbersaw very mobile, meaning he is among the very few heroes who can actually give chase to a fleeing Slark.

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

* Reactive Armor helps Timbersaw sustain harassment from Stifling Dagger, as well as ganking attempts.
* Phantom Assassin is a hero with moderate HP pool, and usually appears in the front line of battle. Because Blur does nothing against spells, she is vulnerable to Timbersaw's skills.
* Timbersaw can easily escape from Phantom Assassin thanks to his Timber Chain.
Additional:
* Reactive Armor helps Timbersaw sustain harassment from Stifling Dagger.
* Phantom Assassin has a moderate health pool and usually appears in the front line of battle, making her vulnerable to Timbersaw's magic burst.
* Timbersaw can easily escape from Phantom Assassin thanks to his Timber Chain.

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

* The burst damage from Timbersaw's abilities is more than enough to deal with Enchantress and her creeps.
* Timbersaw doesn't rely on his physical attacks, which makes Untouchable useless against him.
* Timber Chain can close the gap between them and minimize damage from Impetus.
* Be aware, however, that Timber Chain could work against him if used to escape.
* However, Impetus can ignore Reactive Armor if Enchantress is not a primary target for Timbersaw or if he is disabled.

* Timbersaw is often too mobile and durable for Gyrocopter to bring down with his area attacks.

* 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.

* Timbersaw can easily cut down the tree that Monkey King is standing on, stunning him for a lengthy period.
* Timbersaw can use Timber Chain to easily escape Wukong's Command and Primal Spring's slow.
Additional:
* Timbersaw's low cooldown and low mana cost abilities destroys the trees that Monkey King depends on.
* Timber Chain allows Timbersaw to escape Wukong's Command.

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

* 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.

* The percentage-based primary-attribute reduction effect of Whirling Death can be devastating for Pudge due to his high strength gain through Flesh Heap.
* Reactive Armor's health regeneration and common itemization for magic resistance and durability make Timbersaw a poor target for Pudge.
* Timber Chain's high mobility makes Timbersaw difficult to lockdown for Pudge, given he only has one reliable disable.

* Heroes that can close the gap can easily chase her down, such as Timbersaw with Timber Chain and Anti-Mage with Blink.

* 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.

* 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.

* 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

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

* 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.

* 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.

* Timbersaw relies on dealing massive amounts of pure damage, making Cold Embrace a good setup for his nukes.
* If he has Reactive Armor stacks, Timbersaw can tank the damage from his allies if he is targeted by Winter's Curse. If he's not the target, Timbersaw's abysmal attack damage will contribute next to nothing when he is cursed to attack an ally.

* 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.

* 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 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.

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

* 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 preventing Bounty Hunter from using all of his spells.

* 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.

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

* 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.

* 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.

* 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.

* 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.

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

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

* Timbersaw: Lone Druid will have a hard time dealing with Timbersaw due to his tankiness and high Armor from Reactive Armor

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

* 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.

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

* Heroes who are not easily crippled by Fate's Edict or Fortune's End, such as Timbersaw, or those who can dispel them, such as Phantom Lancer, can kill Oracle unhindered.

* 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.

* Reactive Armor makes Timbersaw very effective against heroes that control a lot of units, such as Broodmother, Lycan and Undying.

* 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.

* 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.

* Heroes that have AoE damage: Lina, Keeper of the Light, Timbersaw, Leshrac, Bristleback, Axe

Additional:
* Timbersaw can easily cut down trees from Sprout, making it very difficult for Nature's Prophet to teleport away or trap enemies.
* Timbersaw's abilities quickly clear out treants.
* Reactive Armor negates most of the damage of Nature's Prophet's treants, and Timbersaw can often allow himself to be attacked in order to heal himself.

* Timbersaw can take down Terrorblade's illusions with his area damage burst.
* Reactive Armor plus another armor item reduce much of Terrorblade's damage.
Additional:
* Timbersaw's spell combos all deal magical and pure damage, completely ignoring Terrorblade's high base armor and clearing his illusions very quickly due to the AoE damage.
* Reactive Armor negates most of Terrorblade's damage against Timbersaw, and its high health regeneration and armor bonuses can help Timbersaw survive after being Sundered.

* All Timbersaw's abilities are AOE pure damage and can easily deal with Phantom Lancer's illusions
* Reactive Armor highly negates Phantom Lancer's physical damage, making him having a hard time killing Timbersaw.
Additional:
* Phantom Lancer's lack of burst damage and constant attacks will increase Reactive Armor to max level immediately. Coupled with Timber Chain making escaping from crowds easy, it is almost impossible for Timbersaw to be killed by Phantom Lancer.
* Whirling Death and Chakram can instantly destroy large groups of illusions, negating Phantom Lancer's advantage.

* 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.

* 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.

* Timbersaw's innate tankiness is very hard to deal with as Naga Siren. Timbersaw's high Pure Damage and spammable AoE nukes can also destroy Naga Siren's illusions very fast.

* 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.

* Reactive Armor makes Timbersaw very effective against heroes that control a lot of units, such as Broodmother, Lycan and Undying.

Additional:
* All of Timbersaw's spells deal AoE damage, killing Lycan's summons very quickly.
* Reactive Armor will gain stacks quickly because of Lycan's summons.

* 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.

* 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.

* Spiderlings deal almost no damage against Reactive armor. They also die quickly from Timbersaw's AoE abilities.
* Broodmother has no mobility ability except the movement speed buff from Spin Web, allowing Timbersaw to easily escape her Incapacitating Bite with Timber Chain.
* Timbersaw's tree-cutting abilities makes it difficult for Broodmother to hide, especially near the edges of the map.
Additional:
* Reactive Armor prevents Broodmother's spiderlings from being able to effectively harass Timbersaw in the lane.
* Timber Chain's high mobility makes Incapacitating Bite's slow irrelevant.
* Timbersaw's abilities can destroy any trees that Broodmother attempts to hide in and his AoE abilities can quickly clear her Spiderlings.