Ava's Arctic Armour

You summon a protective wall of ice that surrounds you and up to 1 other person. The wall gives any character inside full cover and lasts until the end of the caster's next turn. The wall has an AC of 12 and 40hp, it is immune to poison and psychic damage and vulnerable to fire damage. If the wall is reduced to zero hit points before the end of the caster's next turn the wall shatters outwards. Everything within a 20ft radius must make a dexterity saving throw or take 2d6 cold damage. If the wall isn't reduced to zero hit points before the end of the caster's next turn then the wall shatters outwards and everything within a 20ft radius must make a dexterity saving throw or take 5d6 cold damage.

At higher levels the damage caused by the wall shattering increases by 1d6 for every level above 3rd.