Deplete

You attempt to drain a creature in the process of casting a spell. If the creature is casting a spell with a spell slot higher than the unmodified spell level, reduce the spell by 1 level (minimum being the base level of the spell).

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, reduce the spell level by an additional 1 for each spell slot higher used in the casting. (minimum being the base level of the spell).