Twitch
What to Keep:
I think that his Q-Ambush, W-Venom Cask, and R-Spray and Pray should stay as they form a great kit. Even his E-Contaminate should stay as it is but I would move his P-Deadly Venom as part of his E Passive as they would make sense since they mainly are so chained together. This would mean that a whole new Passive would have to come in play.
What to Change:
NEW P-Caustic Bombs: whenever Twitch kills or assists in a kill of a champion, an immediate toxic bomb would cloud in an area around the champion's body dealing damage on the explosion, applying Venom, and a dot damage for every second spent inside the cloud. This would last for around 10s which would fit how Twitch wants to spread his plague while giving him a way to have another form of damage.