Acid Armor

You partially transmute your body into acid.  Until the spell ends, you have resistance to acid damage as well as nonmagical bludgeoning, piercing, and slashing damage, and a creature that hits you with a melee attack while within 5 feet of you must make a Dexterity saving throw, taking 2d8 acid damage on a failure or half as much on a success. 

At Higher Levels.  When you cast this spell using a spell slot of 6th level or higher, the acid resistance becomes immunity and the acid damage increases by 1d8 for each slot level above 5th.