Viper counter and synergy picks

Power Treads

A core Boots upgrade to improve your mobility and damage output with attack speed and stats. The attack speed gain lets you quickly build up Poison Attack stacks for more damage and slow on enemy heroes. Also lets you conserve mana through stats toggling.

Blade Mail

A core item to use your tankiness in the early game and return a ton of damage along with Corrosive Skin. The item only gets better as you get more tanky with items like Shiva's Guard and Rod of Atos.

Aghanim's Scepter

A mid to late game pick up to apply Nethertoxin and Corrosive Skin on enemy heroes around you. Also works as a mobility tool to jump in or out of fights.

Shiva's Guard

A core item to gain some much needed armor to stand in the middle of fights and dish out increased damage with your spells and Poison Attack right clicks. Also reduces the tankiness of enemy heroes around you by reducing their HP regen and lifesteal.

Aghanim's Shard

A core upgrade for Poison Attack to deal more damage to enemy heroes and buildings with minus armor. Also helps you take Roshan faster.

Bloodstone

A core item to lifesteal back up in the middle of fights with your massive damage through spells and Poison Attack right clicks. Also provides a basic dispel on cast. Has great synergy with the Caustic Bath facet to do massive damage and heal back up while standing in your Nethertoxin.

Black King Bar

A core item to avoid most disables and silences on the enemy team to use your spells and hit freely in fights. Also improves your right click damage and tankiness through HP pool and magic resistance.

Mage Slayer

A core item that increases your damage output while providing some much needed tankiness and mana regen. Also reduces the spell damage of enemy heroes you attack with right clicks.

Sange and Yasha

A core item that makes you significantly more tanky and provides some much needed mobility and attack speed. The status resistance also makes it harder to kite or lock you down.

Hurricane Pike

A core mobility item that also increases your attack range to hit enemy heroes and buildings from further away. Works well to put some distance between you and an enemy hero and hit them with infinite range for a short period with the Hurricane Thrust active.

Eye of Skadi

A late game pick up to significantly increase your tankiness and damage through stats. Works well against lifesteal and high HP regen on enemy heroes. Reduces the movement speed and HP sustain of enemy heroes you hit to make them less tanky and keep chasing them.

Ring of Regen

Gives you HP sustain to stay in the lane and not get zoned by Viper's constant damage from Poison Attack right clicks and spells.

Wind Lace

Gives you movement speed to kite or close the gap on Viper. Also counters the movement slow from Poison Attack, Corrosive Skin, and Viper Strike.

Boots of Speed

Gives you movement speed to kite or close the gap on Viper. Also counters the movement slow from Poison Attack, Corrosive Skin, and Viper Strike.

Cloak

Gives you magic resistance to significantly reduce the damage taken from Viper's Poison Attack right clicks and spells.

Ring of Health

Gives you HP sustain to stay in the lane and not get zoned by Viper's constant damage from Poison Attack right clicks and spells.

Lotus Orb

Lets you dispel the Poison Attack stacks off yourself or an ally. Also lets you reflect Viper Strike back onto Viper.

Mage Slayer

Provides magic resistance and reduces the damage dealt by Viper from all his spells to nullify his burst potential.

Pipe of Insight

Gives you and your team magic resistance and barrier to significantly reduce the damage taken from Viper's Poison Attack right clicks and spells.

Eternal Shroud

Gives you magic resistance to significantly reduce the damage taken from Viper's Poison Attack right clicks and spells.

Black King Bar

Gives you debuff immunity and magic resistance to avoid the movement and attack speed slow from Viper's spells as well as reduce the damage taken from his Poison Attack right clicks and spells.

Heaven's Halberd

Provides evasion and lets you disarm Viper to prevent him from right clicking freely in fights with Poison Attack.

Force Staff

Gives you a repositioning tool to kite Viper and push yourself or an ally to safety when slowed by Viper Strike and Poison Attack right clicks.

Glimmer Cape

Gives you magic resistance and barrier to significantly reduce the damage taken from Viper's Poison Attack right clicks and spells as well as save yourself or an ally slowed by his spells.

Abyssal Blade

Gives you an instant lockdown against Viper and burst him down with a possible chain stun before he can impact fights or disarm you and get away using Nosedive.

Butterfly

Gives you armor and evasion to defend yourself against Viper's Poison Attack right clicks with the tankiness and miss chance.