it's a 3-level Prestige Class from Fiendish Codex II. Its signature ability is Hellfire Blast, which adds +2d6/class level to your Eldritch Blast at the cost of taking 1 Con damage to yourself per shot.<br/><br/>Combine with the 1st-level Binder Vestige that gives Ability Fast Healing 1, and it's a free 6d6 in perpetuity.