Abyss

The Abyss features an endless variety of evil - shaped as an endless number of layers, one atop the other, the Abyss stretches into infity, though some Faerûnian scholars have theorized that the plane has no more than 666 layers. But this unknown, as no travellers have been known to return from anywhere below a two hundred-odd layer.

Each layer is different from all the others, the only apparent similarity being that the plane seems to try and inflict as much harm on travelers with each layer as possible, it might even be said that the plane is as varied and evil as the demons who inhabit the plane. No deities dwell in the Abyss, although the 66th layer used to be home to the Demonweb Pits and the drow pantheon (excluding Eilistraee who makes her home in Arvandor) but the Demonweb Pits were torn out of the Abyss and became a seperate outer plane, following the Silence of Lolth.

The only constant in this chaotic relam is the presence of the adjacent Blood Rift where the demons fight their mortal enemies the devils. The proximity of the Blood Rift to both the Abyss and the Nine Hells allows for the demons and devils to wage an unceasing war upon each other. But unlike the Nine Hells which is always connected to the Blood Rift by it's top most layer (called Avernus), the ever shifting nature of the Abyss brings different layers into proximity with the Blood Rift at different times, allowing the Demons to constantly bring fresh forces to bear in ther constant struggle known as the Blood War.

Abyss Links
Various layers of the Abyss include portals to the Demonweb Pits, Besheba's realm in the Barrens of Doom and Despair, Hruggek's realm in Clangor, the realm of Urdlen in Hammergrim and the Fugue Plane. Portals also exist to other planes like the Deep Caverns and Fated Depths, and indeed the River of Blood flows through the Abyss and into most of the other Fiendish Planes.

Abyssal Petitioners
When demons steal souls from the Fugue Plane and bring them to the Abyss, those souls become petitioners called manes. A mane has pale white skin, cruel claws, sharp teeth, sparse hair and white eyes. The few manes that survive for many years are sometimes "promoted" to lesser demon types like imps, though they retain no memory of their former lives.

Manes have the following qualities: Additional Immunities:' Electricity, poison. Resistances: Acid 10, fire 10. Other Special Qualities: Acidic vapor, no planar commitment
 * Acidic Vapor (Su): When a mane is slain, it discorporates into a cloud of noxious vapor. Every creature within 10 feet of a slain make must make a successful DC 20 Reflex save or take 1d6 points of acid damage.
 * No Planar Commitment (Ex): Unlike most other petitioners, manes can leave the plane they call home.

The Abyss has no divine realms, and no true deities make their home there. However, a great many demon princes - vie for power and territory on this plane. A few prominent such beings are Demogorgon, Eltab, Yeenoghu, Orcus, Graz'zt, Baphomet and Kostchtchie.