Quote Originally Posted by MwaO View Post
Spiderkissed and Mordant weapons do that.

Just be aware, having damage be poison creates some issues with immunity to poison, which is reasonably common. Venom Hand Master resolves that. Venom Hand Assassin is a good bonus damage feat if you get that. And Skulker of Vhaeraun is essentially Sarifal Feywalker for Drow poison wielders.
Only sort of. It requires Weapon attacks, which is a bit of a drag for a number of characters, particularly actual Assassins.