Erevan's Nightfire

You conjure black flames with a violet core that devour light and life. Choose a point within range; the flames erupt in a 15-foot-radius sphere centered on that point. Each creature in that area must make a Dexterity saving throw. On a failed save, a creature takes 3d8 necrotic damage and 3d8 fire damage, and it can’t regain hit points until the end of its next turn. On a successful save, a crea ture takes half as much damage and suffers no additional effects.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the necrotic and fire damage each increase by 1d8 for each slot level above 3rd.