When you cast a level 1+ spell with casting time of an action that forces a target to make a saving throw, you can "ferment" the spell. The spell's saving throw becomes Constitution for this casting. On a failed save against the spell, a creature has the Poisoned condition until the end of your next turn.
You can use this feature a number of times equal to your Intelligence modifier (minimum of once) and regain all expended uses when you finish a Long Rest.