Rockslide
The ground within a 40-foot radius heaves and splits. Each creature in the area makes a Dexterity saving throw against your spell save DC. On a failure it takes (H + half your level)d12 bludgeoning damage and is knocked Prone. On a success it takes half damage and stays standing.
The broken ground is difficult terrain for 10 minutes. Structures and unattended objects in the area take double damage.
AFTERSHOCK. As a lair action at initiative 20, the ground convulses again. Every creature still Prone inside the area takes 4d8 bludgeoning damage, and every other creature in the area makes a Dexterity saving throw against your spell save DC or is knocked Prone.

