Limbo

From Manual of the Planes (3e):

It is where everything, and nothing, is possible.

It is where raw chaos seethes.

It is where the elements come to die.

Limbo is a plane of pure chaos.  Untended sections appear as a roiling soup of the four basic elements and all their combinations.  Balls of fire, pockets of air, chunks of earth, and waves of water battle for ascendance until they in turn are overcome by yet another chaotic surge; however, landscapes similar to ones found on the Material Plane drift through the miasma:  bits of forest, meadow, ruined castles, and small islands.

Limbo is inhabited by living natives.  Most prominent of these are the githzerai and the slaadi.  In Limbo, most petitioners take the form of unthinking, ghostly spheres of swirling chaos.

Limbo has no layers.  Or if it does, the layers continually merge and part, each is as chaotic as the next, and even the wisest sages would be hard-pressed to distinguish one from another.

Permanent portals exist between various planes and Limbo; however, a huge ball of fire, a pile of boulders, or a terrible windstorm could surround the Limbo side of the portal.  Thus, entering limbo can be quite dangerous for visitors unprepared to deal with the plane of chaos.

Slaadi and githzerai are commonly associated with Limbo.  Of the two, only the slaadi have been natives since time began.  The githzerai arrived far later, seeing the entire plane as a challenge to their indomitable spirit.  Limbo is also a harsh proving ground for their particular ethos:  "Pain is weakness leaving your body."

Even though they're natives, slaadi control Limbo just like travelers do; however, a slaad's control never falters even if the slaad is unconscious, and the are of control surrounds the slaad tightly.  To viewers, it seems as if a slaad lolls unhurt in a bath of fire.

The few githzerai who follow a monastic calling also follow the dictates of law, and such monks are particularly challenged by the chaos of Limbo; however, the strongly chaos-aligned trait of Limbo is neutralized by the walls of great githzerai monasteries.  Most githzerai do not follow a monastic calling and congregate in large cities.

The petitioners of Limbo are those who revere chaos above all else.  Some come to embody the plane, while others linger as insane spirits composed of shifting limbo-stuff.

Limbo is filled with wonders beyond count, a few of which are briefly presented below. Random surges of elemental fire light the plane. Some are far off and visible only as a dim glow spreading through floating seas, while others are bright, too-close suns. The random boil of Limbo sometimes limits vision to nothing (inside an earth-dominant area, for example), but other times vision can stretch for miles through contiguous air-dominant areas.

There is no day or night on the plane of Limbo.