Abyss-Bound Soul( Fiendish Codex I: Hordes of the Abyss, p. 83)
You have pledged your immortal soul to a particular demon lord in return for a gift that aids your evil works in life.
Your evil brand incorporates the personal symbol of your demon lord patron, who watches over you from the Abyss. You gain a +2 bonus on saving throws made against spells with the good descriptor. Additionally, a tiny portion of your patron's power infuses your body, granting you an additional benefit. The exact benefit gained depends on who your patron is, as given below. Baphomet: You deal double damage with weapons when you charge. Dagon: You can breathe water as well as you can breathe air. Demogorgon: Once per day, you can automatically summon a tanar'ri with a CR equal to or less than one-half your character level. The summoned demon follows your commands and remains at your side for up to 1 hour. This ability is the equivalent of a spell cast at a level equal to your character level. Fraz-Urb'luu: You cast illusion spells at +1 caster level. Graz'zt: You have immunity to fear effects. Juiblex: You gain resistance to acid 5 (or your current resistance to acid increases by 5). Kostchtchie: You gain resistance to cold 5 (or your current resistance to cold increases by 5). Malcanthet: You cast enchantment spells at +1 caster level. Obox-ob: Your natural armor bonus increases by 1. Orcus: You cast necromancy spells at +1 caster level. Pale Night: You have immunity to insanity and confusion effects. Vazuzu: While flying, you gain a +2 profane bonus on Reflex saves. Yeenoghu: When you attack with natural weapons, you gain a +1 profane bonus on attack and damage rolls. Zuggtmoy: You ignore extra damage from critical hits and sneak attacks 25% of the time.
When you die, your soul becomes the personal plaything of your demon patron. You can be restored to life only by true resurrection, miracle, or wish.