You create a 30-foot-radius sphere of pulsing, luminous purple mist centered on a point you choose within range. This area is heavily obscured. When a creature enters the spell’s area for the first time on a turn or starts its turn there, that creature must make a Constitution saving throw, taking 5d12 necrotic damage on a failed save or half as much damage on a successful one. Creatures are affected even if they hold their breath or don’t need to breathe. After leaving the mist, the creature takes 5 points of necrotic damage per round until it succeeds on a Constitution saving throw or dies.