Abyssal soil

The top two feet of the ground in a 20-foot square centered on a point within range changes into boiling, poisonous mud for the duration. The mud is thick, and makes the area into difficult terrain. When the spell ends, the ground in the area goes back to the way it was before.

Any creature that starts its turn in the area takes 3d6 fire damage. Any creature that ends its turn in the area must make a Constitution saving throw, taking 3d6 poison damage on a failed save, or half as much damage on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, both instances of damage increase by 1d6 for each slot level above 3rd.