Curse of the behemoth

you harness the consuming power of the behemoth in a 25-foot-radius sphere from a point within range. Each creature that starts its turn in that area must make a Constitution saving throw. A target takes 5d6 necrotic damage on a failed save, or half as much damage on a successful one. as a action on your turn you can move the area up to 30ft. 

At Higher Levels. When you cast this spell using a spell slot of 7th level or higher, the damage increases by 1d6 for each slot level above 7th.