Weiss's Ice Prism

A bright white streak flashes from your pointing finger to a point you choose within range and then shapes into a Prism that erupts into an explosion of ice and frost. Each creature in a 20-foot-radius sphere centered on that point must make a Constitution saving throw. A target takes 6d6 cold damage on a failed save, or half as much damage on a successful one. Additionally on a failed saving throw each creature haves its movement speed reduced by half. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd. If this spell is cast at 6th level or higher their movement speed reduced to 0 on a failed saving throw.