Disciple of Darkness( Book of Vile Darkness, p. 49)
The character formally supplicates himself to an archdevil. In return for this obedience, he gains a small measure of power.
Once per day, while performing an evil act, the character may call upon his diabolic patron to add a +1 luck bonus on any one die roll.
Once a character takes this feat, he may not take it again; he may not be the disciple of more than one devil. Nor may he take the Thrall to Demon feat.