The Abyss

The Abyss embodies all that is perverse, gruesome, and chaotic. Its virtually endless layers spiral downward into ever more appalling forms.
Each layer of the Abyss boasts its own horrific environment. Although no two layers are alike, they are all harsh and inhospitable. Each layer also reflects the entropic nature of the Abyss. In fact, much of what one sees or touches on the plane seems to be in a decaying, crumbling, or corroded state.

Optional Rule: Abyssal Corruption

A non-evil visitor that finishes a long rest in the Abyss must make a DC 10 Charisma saving throw. On a failure, the creature becomes corrupted. Refer to the Abyssal Corruption table to determine the effects of this corruption. You can substitute different corruption effects of your own creation.
After finishing a long rest, a corrupted creature can make a DC 15 Charisma saving throw. On a successful save, the corruption effect ends. A dispel evil and good spell or any magic that removes a curse also ends the effect.
If a corrupted creature doesn’t leave the plane within 1d4 + 2 days, its alignment changes to chaotic evil. Casting the dispel evil and good spell on the creature restores its original alignment.

d10	Result
1-4	Treachery. The character gains the following flaw: “I can only achieve my goals by making sure that my companions don’t achieve theirs.”
5-7	Bloodlust. The character gains the following flaw: “I enjoy killing for its own sake, and once I start, it’s hard to stop.”
8-9	Mad Ambition. The character gains the following flaw: “I am destined to rule the Abyss, and my companions are tools to that end.”
10	Demonic Possession. The character is possessed by a demonic entity until freed by dispel evil and good or similar magic. Whenever the possessed character rolls a 1 on an attack roll, ability check, or saving throw, the demon takes control of the character and determines the character’s behavior. At the end of each of the possessed character’s turns, he or she can make a DC 15 Charisma saving throw. On a success, the character regains control until he or she rolls another 1.

Important Layers

The layers of the Abyss are defined by the demon lords who rule them, as the following examples illustrate.

The Gaping Maw

Demogorgon’s layer in the Abyss is a vast wilderness of savagery and madness known as the Gaping Maw, where even powerful demons go insane with fear. Reflecting Demogorgon’s dual nature, the Gaping Maw consists of a massive primeval continent covered in dense jungle, surrounded by a seemingly endless expanse of ocean and brine flats. The Prince of Demons rules his layer from two serpentine towers, which emerge from a turbid sea. Each tower is topped with an enormous fanged skull. The spires constitute the fortress of Abysm, where few creatures can venture without descending into madness.

Thanatos

If Orcus had his way, all planes would resemble his dead realm of Thanatos, and all creatures would become undead under his control. Under its black sky, Thanatos is a land of bleak mountains, barren moors, ruined cities, and forests of twisted black trees. Tombs, mausoleums, gravestones, and sarcophagi litter the landscape. Undead swarm across the plane, bursting from their tombs and graves to tear apart any creatures foolish enough to journey here. Orcus rules Thanatos from a vast palace known as Everlost, crafted of obsidian and bone. Set within a howling wasteland called Oblivion’s End, the palace is surrounded by tombs and burial sites dug into the sheer slopes of narrow valleys, creating a tiered necropolis.

The Demonweb

Lolth's layer is an immense network of thick, magical webbing that forms passageways and cocoon-like chambers. Throughout the web, buildings, structures, ships, and other objects hang as if caught in a spider’s snare. The nature of Lolth’s web creates random portals throughout the plane, drawing such objects in from demiplanes and Material Plane worlds that figure into the schemes of the Spider Queen. Lolth’s servants also build dungeons amid the webbing, trapping and hunting Lolth’s hated enemies within crisscrossing corridors of web-mortared stone.
Far beneath these dungeons lie the bottomless Demonweb Pits where the Spider Queen dwells. There, Lolth is surrounded by her handmaidens—yochlol demons created to serve her and which outrank mightier demons while in the Spider Queen’s realm.

The Endless Maze

Baphomet’s layer of the Abyss is a never-ending dungeon, the center of which holds the Horned King’s enormous ziggurat palace. A confusing jumble of crooked hallways and myriad chambers, the palace is surrounded by a mile-wide moat concealing a maddening series of submerged stairs and tunnels leading deeper into the fortress.

The Triple Realm

The Dark Prince Graz’zt rules over the realm of Azzagrat, which encompasses three layers of the Abyss. His seat of power is the fantastic Argent Palace in the city of Zelatar, whose bustling markets and pleasure palaces draw visitors from across the multiverse in search of obscure magical lore and perverse delights. By Graz’zt’s command, the demons of Azzagrat present a veneer of civility and courtly comity. However, the so-called Triple Realm holds as much danger as any other part of the Abyss, and planar visitors can vanish without a trace in its mazelike cities and in forests whose trees have serpents for branches.

Death Dells

Yeenoghu rules a layer of ravines known as Death Dells. Here, creatures must hunt to survive. Even the plants, which must bathe their roots in blood, snare the unwary. Yeenoghu’s servants, helping to sate their master’s hunger as he prowls his kingdom seeking prey, capture creatures from the Material Plane for release in the Gnoll Lord’s realm.

Type

Dimensional plane