Bubble Swarm

a 25ft sphere centered on a point in range fills with swirling bubbles that burst forcefully on contact. Creatures entering the arena for the first time or on there turn must make a dextarity saving throw. targets take 1D8 cold damage and 1D8 bludgeoning damage, and there speed is reduced by 10 on a failed save, or half as much damage and no additional affect on a successful save