Aside from massive damage and magic resistance reduction, this spell is your main farming tool. You just need to max it out early and start farming nearest jungle camp and lane at the same time

Poison attack makes a strong laner out of Viper. You don't really need to level this up more than once, but it's still pretty important to have early on to zone opponent out of lane without drawing aggro from creeps

Early tankiness solution and another spell that can be useful for farming

Massive magic damage (especially in combination with nethertoxin) and undispellable slow. It's almost reliable kill early on except it's possible to TP out from it

+{s:bonus_damage} Viper Strike DPS : Since you're doubling down on magic damage, it sounds convinient to significantly amplify your ult

+{s:bonus_damage} Corrosive Skin Damage Per Second : Considering you're playing as a tanky frontliner, there aren't much use from attack range, but having a bit more slow, damage and magic resist will do some work

+{s:bonus_max_damage} Nethertoxin Min/Max Damage : Considering Nethertoxin's cooldown it's usually good idea to make it also AoE silence which will also help against a lot of heroes in fights

ALTERNATIVE: Power Treads

Additional mobility and cheap stats. Early Force Staff works well when you're playing against AoE silences, terrain lockdowns or struggle to get into attack range to enemy

Against hard disables and silences (if lotus doesn't work)

ALTERNATIVE: Boots of Travel

Before Black King Bar

Before Black King Bar

Against light disables (like slows and silences) in case you are not the only one struggling from them

ALTERNATIVE: Eternal Shroud

Doubling down on your magic tank role by amplifying your armor, magic damage and increasing your crowd control abilities by standing in the middle of a fight

Before Black King Bar

More of an utility replacement for both Butterfly and Shiva's Guard. It helps with both tankiness, pushing and physical damage output, while also fitting theme of a walking tank

Additional reliable lockdown

Great DPS item for hybrid tank core transition

Nice addition to Buttterfly if you're playing against tanky cores or want to burst enemies down

Great addition for hybrid core. It also allowes you to become a decent damage dealer and pusher. It's also a great addition to +120 damage talent

More of a defensive replacement for Drum or KaYasha, usually good when you need some mobility and stats

Against high attack speed cores, high physical damage lineups or summons