Devil's Flesh( Fiendish Codex II: Tyrants of the Nine Hells, p. 82)
Your skin thickens and assumes a scaled, leathery texture that turns aside blows but serves as a clear mark of your taint.
Devil's Favor (FCII) , CON 15,
You gain a bonus to your natural armor and on Intimidate checks equal to half the number of devil-touched feats you have selected, including this one. If you do not have a natural armor bonus, this feat provides you with one. If you already have one, this feat improves your existing bonus. In addition, you take a penalty on all Diplomacy checks against good creatures equal to the natural armor bonus provided by this feat.