Viper has always been a really strong hero mid, many players struggle to play against this hero in lane as they do not understand the source of the hero’s damage. Viper’s gameplay at level 1 is very simple, Get one level of poison attack, poison the enemy hero once, and get 2 hits in. This poison does not only disrupt the opponent’s movement speed, but also slows down opponent attack speed; making it almost impossible to be efficient at trading hits with him.
This, paired with his new buff on the first skill (+Damage for % of health loss), makes most invoker players not being able to do much against him not just in the earlier levels, but even after level 7+. His 3rd skill which negates 25% of magical damage when maxed out (which most players will) makes it impossible to kill him even with the 4 Skill Combo (Snap>Tornado>Meteor>Deafening Blast). So what should an Invoker do when laning against a viper?
My advice would be first play an Quas Exort Voker. Why? The only way that I have deduced to be best when playing against a good viper would be to outfarm him in lane. This means getting more CS and denies than the viper will (viper is pretty bad when it comes to cs-ing compared to Exort Voker), and outlevelling him in the lane. Still, A level 6 Viper can easily solo kill a Level 7 Invoker easily with Viper Strike, so how do we deal with that? First of all, Viper strike itself will not be enough to down an Invoker that is higher level thatn the Viper. The basis of getting a kill with Viper is that he gets them to a low HP by chipping them with his first skill; thus when he goes for the Viper Strike his first skill deals humongous amounts of damage.
To counter this, control your lane well and play the creeps closer to your highground if you can (which is easy since Exort Invoker has really high damage), secondly do NOT be stingy when it comes to regeneration. Whenever Viper walks up front to get a hit in, use forge spirits and cold snap to trade him with you standing on the highground. This will force the Viper to go back after getting at max 2 hits, making it an inefficient trade whenever he tries to harrass you. Your added Quas should give you around +20HP regen at level 3, and after that you should be safe from Viper as long as your health isn’t too low and am carry a TP (Just TP whenever you’re caught in a bad spot).
Lastly, without proper roaming from teammates, it is fairly difficult to kill a viper if his CS is pretty good. In higher caliber games, Vipers would generally go for a Helm of Dominator in the early game, alongside treads. If opposing viper goes for this build, it is impossible to kill him in the lower levels. If you do wish to go for a kill, the best way to do so would be the Alac+Snap+Wall+Forge Combo, reducing his MS, AS, and armour rendering him more unlikely to turn on you.