As an action, extreme cold afflicts a creature that you can touch or see within 10 meters. At the start of each of its turns for the duration, the creature must make a Fortitude saving throw.
On a failure, it takes 3d8 cold damage and is slowed 1 until the end of its next turn.
On a critical failure, it takes twice as much damage and is slowed 2 until the end of its next turn.
On a success, it takes half as much damage and and the effect ends.
On a critical success, it takes no damage and the effect ends.
You can increase the damage by 3d8 for each additional mana expended.