One creature you can see, Black crystalline frost forms over the target. The target must make a Constitution save. On a failed save, the target takes 4d6 cold damage and their speed is reduced by 5 feet. If pass, take half damage and spell effects end.  At the beginning of each of its turns, the target makes a Strength saving throw. If it fails, they take 2d6 necrotic damage and their speed is reduced by an additional 5 feet. If their speed is reduced to zero, they are restrained.  If they pass, they take half damage for that turn and spell effects ends.