Dark Side of the Moon

A 30-foot-radius sphere of magical darkness appears into existence, centered on a point you choose within range. The sphere remains for the spell's duration. Each creature in the sphere when it appears must succeed on a constitution saving throw, taking 5d10 cold damage on a failed save or half if it succeeds. The sphere's space is considered difficult terrain. Additionally, each turn spent in the sphere causes an additional 1d10 cold damage. A creature that spends more than 3 turns in the sphere takes double that.