Crystal Coffin

As a reaction when you take damage, you can entomb yourself in a coffin of crystal ice, which melts away at the end of your next turn. You gain 10 + your spell-casting modifier temporary hit points per spell level expended, which take as much of the triggering damage as possible. Immediately after you take the damage, you gain vulnerability to fire damage, your speed is reduced to 0, and you are incapacitated. These effects, including any remaining temporary hit points, all end when the ice melts.