Walfric's lightning guardian

A protective magical force surrounds you, manifesting as a armor of thunder that covers you and your gear.
You gain 10 temporary hit points for the duration. If a creature hits you with a melee attack while you have these hit points, the creature takes 10 lightning damage. 

When you cast this spell using a spell slot of 2nd level or higher, both the temporary hit points and the lightning damage increase by 5 for each slot