Blood Boil

You cause the blood of your enemies to boil within them. Chose a point within range. Creatures within 15 feet of that point must make a Constitution save. On a failed save they take 3d8 necrotic damage or half as much on a success. As an action, you can repeat this effect on each of your turns for the duration, and you may choose a different point each time.

At higher levels.  If you cast this spell using a spell slot of fifth level or higher, the damage increases by 1d8 for each slot level above 4th.