Wilt

You channel the dark energy within plants to create a 5ft cube of thorny vines that saps away energy from a creature. Any creature in a spell's space when you cast the spell must succeed a DEX saving throw or take d6 void damage. Any creature must also make a saving throw when entering the space for the first time on a turn or ends its turn there. When the creature enters the space or ends its turn there, the creature's speed is lowered by 10ft, and cannot regain health until the start of your next turn.

This spell's damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).