Erythnul is a brutal deity who makes his home in what appears to be a tumbled ruin of some vast citadel. In fact, its tortuous passages channel cold winds on which can always be heard the sound of terrible battle. Battle-mad petitioners of all races infest the passages, and they desire nothing other than to hunt and slay each other in cold blood.

At the center of the pile is Erythnul himself, usually engaged in the slaughter of an endless stream of petitioners, as well as the occasional mortal captive. In battle, the deity's features change between human, gnoll, bugbear, ogre, and troll. If ever Erythnul's blood is spilled, it transforms into an allied creature of whatever form Erythnul currently wears.

No one goes to the Citadel of Slaughter on purpose, unless they serve Erythnul and seek to join in the deity's eternal slaughter.