Drain Magic

The prick of your blade can siphon magic force from Witches. Make a melee spell attack against a creature within your reach. On a hit, the target must make a DC16 saving throw or lose 1d4 spell slots per turn starting with the highest.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the damage increases by 1d4 for each slot level above 6th.