Alder's Entombment

You drop a garnet onto the ground and point to a target area within range. The target area is a 25' cube.

When you cast the spell, any creatures fully in the area are swallowed by the earth below it and placed inside a stone tomb. Any creature not fully in the area and all creatures in the spaces adjacent to the target area must make a DEX save or be knocked prone. The target is blinded, deafened, and restrained and placed 15' underground in a space barely large enough for the creatures. On their turn, any entombed creatures can use their action make a STR check vs your spell save DC. If they fail they take 10d8 magical bludgeoning damage as the rocks crush them. On a success they take half damage, and can use their movement to dig 5' in any direction. Creatures with a burrow speed have advantage on this save. 

Any creatures that remain underground for the full duration of the spell are permanently entombed and begin to suffocate.