Cryo stop

As a reaction, you can attempt to freeze a creature that missed a melee attack against you. The creature that triggered this reaction makes a CON save against your spell save dc. A creature takes 4d6 cold damage on a failed save and becomes entombed in ice, or half as much damage on a successful one and isn't entombed. 
When a creature is entombed, its speed becomes zero and it cant take reactions for 1 round.