Vile Edge Strike
Transmutation cantrip (Sorcerer, Warlock, Wizard)
Casting Time: 1 action
Range: Self
Components: S, M (a weapon with which you have proficiency and that is worth 1+ CP)
Duration: Instantaneous.
You make one attack with a weapon you are wielding. On a hit, the target suffers the weapon attack's normal effects. If the target is not immune to Poison damage, until the start of your next turn, the target has Disadvantage on the next Attack Roll it makes.
Cantrip Upgrade: The attack deals an extra 1d8 Poison damage to the target on a hit when you reach 5th level, 2d8 at 11th level, and 3d8 at 17th level.