Creeping Cold

A shifting cluster of ice forms in your hand. Make a melee spell attack against the target creature. On a hit, the creature is plagued with crawling ice and takes 3d10 cold damage. For the next two rounds, at the start of the creatures turns, it takes an additional 1d10 cold damage. On the third round, at the start of the creatures turn, the ice explodes and deals 2d6 cold damage to every creature within 5 feet of the target, including itself.