The surface of this armor roils with pent-up energy.

A suit of armor that has this property strikes back at foes who hit hard in melee. While wearing retaliation armor, each time you take 10 or more points of damage from a single melee attack, the armor deals 1d6 points of damage to the attacker. If a single melee attack drops your hit points below 0, the armor strikes the attacker for 3d6 points of damage.
Damage from retaliation armor is treated as magic for the purpose of over-coming damage reduction.

Prerequisites: Craft Magic Arms and Armor, symbol of pain.
Cost to Create: 2,000 gp (plus 150 gp for base item), 160 XP, 4 days.