Carbon Fog

You create a cloud of icy fog in a 20-foot-radius sphere centered on a point you can see. The sphere extends around corners, and its area is heavily obscured. The fog is semi-solid, and its area is considered difficult terrain. Each creature that enters the power's area for the first time on a turn or starts its turn there takes 4d6 cold damage and gains 1 slowed level until the end of its turn. The fog lasts for the duration of the power or until it's dispersed by a wind of moderate or greater speed (at least 10 mph).