when does skarner gets a poison passive?

He's not a scorpion, he's a brackern - a scorpion-like magical crystal creature. Although, the debuff applied by his E - Fracture, is called "Crystal Venom".

He has venom, it's his E debuff, as stated above. He used to have another passive that his E stun comes from, where if he used 3 abilities, his next auto would stun you (legit stopped playing him during that time, so idk if i'm right on the way it was applied)

He was kept as a pet in Zaun for a bit and Viktor removed the glands that produced venom

I vaguely remember hearing that Riot hates damage over time.

When I played Heroes of Newerth, there was a hero called "Slither" , his Q was a slow + intermitent damage spell (X amount of damage every 3 seconds for 15 seconds) and his ult was a 12 second AoE DoT that did the most damage in the entire game by a huge margin but could never kill by itself (It left you at 1 HP). These abilities would be completely broken in League but fine in HoN. League just can't handle DoTs very well.

Slither was a bitch to fight against, so I'm rather pleased he doesn't exist here. The only reason it functioned in HoN is because you could deny anyone that was fatally poisoned which you cannot here in LoL.

same time the brand new phenoix gets a revive passive