Black Flame Ritual

You surround yourself in pillars of black flame, burning your surroundings to ash. When you cast this spell, every creature within 15 feet of you must make a Dexterity saving throw. On a failed save, they take 6d6 fire damage, and an additional 2d6 necrotic damage on their next turn. On a successful save, they take half as much damage, and do not take the additional damage on their next turn.