As a reaction, which you use when you are hit by an attack, frost rimes you and your gear.
If the creature who damaged you is within 10 meters it must make a Fortitude saving throw as it is covered in the spectral frost.
On a failed save, it takes 1d10 cold damage and it is slowed 1 until the end of its next turn and has disadvantage on the next weapon attack roll it makes before the end of its next turn.
On a successful save, a creature takes half as much damage and isn’t slowed and doesn’t have disadvantage.
You can increase the damage by 2d10 for each additional mana expended.