Thwomp

Rocks and pebbles gather over a creature in range’s head to form a solid block of stone. The target must make a dexterity saving throw. On a failed save the target takes 1d8 and it’s speed is reduced by 10 ft on a successful one the target takes half as much damage.

When casting Thwomp with a 2nd or higher level spell slot the damage increases by 1d8 for every spell slot over 1st