Burden

You cast a disorientating wave of negative energy towards one large or smaller creature. The target must succeed on an consitution saving throw or take 1d4 psychic damage and subtract 1d4 from the next saving throw it makes before the end of your next turn.

This saving throw penalty increases by 1d4 when you reach certain levels: 6th level (2d4), 12th level (3d4), and 18th level (4d4).