Armor of Avernus

You touch a willing creature, and a protective layer of fiery force surrounds them. Their armor class increases by 2 for the duration, and any creature that hits them with a melee attack takes 2d4 + your spellcasting ability modifier fire damage. The spell ends if the affected creatures is reduced to 0 hitpoints, or is dismissed as an action.

At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d4 for each slot level above 3rd, and the armor class bonus increases by 1 for every second slot level above 3rd.