Chilling Darkness

Magical darkness spreads from a point you choose within range to fill a 30-foot-radius sphere for the duration. The darkness spreads around corners. Nonmagical light, as well as light created by spells of 5th level or lower, can't illuminate the area, and creatures with darkvision can't see through it.
The area inside the darkness is lightly obscured and frigid cold. Any creature that starts its turn within the sphere must succeed a Constitution saving throw. On a failed saving throw, a creature take 4d6 cold damage and its speed is reduced by 20 ft until the start of its next turn. On a success, the creature takes half damage and its speed isn't reduced.