Backlash

Your armor is covered in spikes, or runes that ward you against attacks. Whenever you are hit with a melee attack and are wearing heavy armor, the attacking creature must make a strength saving throw against your strength (athletics) check. On a failed save, the creature takes piercing damage equal to your strength modifier. If you decide that your armor has protective runes, then the damage type is force damage and the amount is equal to your intelligence modifier. You also get to use this feature when an attack roll against you is a natural 1.