Demonic Skin( Fiendish Codex I: Hordes of the Abyss, p. 85)
Your skin has rough, scaly patches that enhance your natural armor.
Your natural armor bonus improves by 1. This improvement increases by 1 for every two Abyssal heritor feats you possess. If you do not have natural armor, assume your natural armor bonus is +0.
Your thickened skin tends to catch on objects and makes you less flexible. Because of these effects, you take a -2 penalty on Escape Artist checks.