Arcane Siphon

You choose a creature you can see within range and place a dark siphon on it. If the creature is not an arcane caster, this spell has no effect. Until this spell ends, whenever the target tries to cast a spell they must succeed on a Charisma saving throw to do so. On a failure, the spell is not executed, their spell slot and respective action are used up, and you restore a number of hit points equal to 10 + the level of the expended spell slot. If the target drops to 0 hit points before the spell ends, you can use a bonus action on a subsequent turn of yours to mark a new creature.