Mabar the Endless Night

Mabar the Endless Night is a blackened realm where the faintest spark of light is quickly devoured by the unending darkness. It is a plane suffused with negative energy and is often positioned as the antithesis of Irian.

Description
Mabar is a realm where no light shines. It is a world that is home to demons and the creatures that go bump in the night. The realm of Mabar is often colloquially cited as why nightmares occur.

On the flip side, priests of the Blood of Vol will also seek out manifest zones of Mabar, to build shrines and allow access to more powerful spells. In addition, a secretive sect of druids in the Eldeen Reaches called the Nightbringers also worship Mabar, and seek out manifest zones, especially in the Gloaming.

Mabar and Mabar manifest zones are thought to be responsible for Mabar Crystals, inky black crystals that empower negative energy spells.

Inhabitants

 * The most populous of the denizens of Mabar are the yugoloths. Other fiends, such as barghests, kastighur, and succubi, also call Mabar home.
 * Creatures of shadow are spawned from Mabar, like nightshades, shadow mastiffs, and trillochs'''.
 * Some forms of undead are thought to haunt Mabar, including bodaks, various nightshades, necronauts, shadows, and vasuthants
 * I have found records of creatures known as death giants that are bound to the plane of Mabar itself.

Manifest Zones

 * In the Eldeen Reaches, a section of the Towering Wood called The Gloaming is a manifest zone, resulting in disfigured trees, corrupted vegetation, and horrid animals.
 * The Shanjueed Jungle on the continent of Sarlona was claimed to contain to a manifest zone to Mabar on initial survey, but none have returned to confirm.

Coterminous
The nights grow blacker and more dangerous when Mabar becomes coterminous with Eberron. Legends say that travel to Mabar becomes as easy as stepping into an area where there is absolutely no light, and inhabitants of the plane can slip out from the shadows and into the world. The plane is thought to become coterminous on the three nights of the new moon closest to the winter solstice once every five years or so.

Remote
When Mabar is remote, the darkness on Eberron seems less deep and nights less fearsome. The moons in the sky seem to reflect more and bathe the nights in natural moonlight. These periods most often occur every five years or so on the three nights around the full moon nearest the summer solstice.