Spike Skin

You touch a willing creature, causing its skin to harden and form spiky protrusions. The target gains resistance 4 to all physical damage (except adamantine).

Whenever a creature damages the target with an unarmed attack or non-reach melee weapon, the attacking creature takes ] damage.

This impulse lasts for 10 minutes, but each time the target takes physical damage, the duration decreases by 1 minute. The target is temporarily immune to this impulse for 1 hour. If you use Spike Skin again, any previous one ends.

Level (+2) The resistance and damage each increase by 2.