Chromatic Armor

You sheathe a creature (including yourself) in elemental energy. 

Select one creature within range.  Choose one damage type from this list:  acid, cold, fire, lightning, or thunder.  If the creature targeted by this spell is hit by a physical melee attack before the start of your next turn, the attacking creature takes 1d6 damage of the selected type.

The spell's damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6)