Styx

The Styx, also written as the River Styx, linked the topmost layers of the Lower Planes. Those who touched or drank from the Styx would forget their past lives completely for a while, sometimes permanently.

Cosmology
The Styx crawled through the uppermost layers of the seven lower planes, as described by the Great Wheel cosmology model: Acheron, the Nine Hells, Gehenna, Hades, Tarterus/Carceri, the Abyss, and Pandemonium. Its headwaters and many tributaries began in the uppermost layer of Pandemonium. In Avalas, top layer of Acheron, the Styx would emerge from a crate on one cube, run for miles, drain down into another crate, and reappear on a different cube entirely. Sometimes, it changed course and drowned whole cities, taking memories and lives. The Styx wound around the Plain of Infinite Portals, first layer of the Abyss; some channels poured into pits, and foul water welled up out of other pits and joined the Styx. On Orthrys in Carceri, it mingled with the canals and bogs and soaked the ground with its magic. On Khalas in Gehenna, the Styx was the greatest river there, rushing through canyons and gorges at shocking speed and over enormous waterfalls. It was incredibly dangerous to sail here. On Avernus in the Hells, streams of blood from all the battles there flowed into the Styx. Tributaries or branches of the Styx crawled onto their lower layers as well. For example, the Styx connected to the fifth level of the Nine Hells, Stygia, where it cut a channel through the great frozen sea. It was the only open water here, but was choked with icebergs and filled with sahuagin and fiendish sharks that attacked the boats. Still more streams beyond count trickled all the other layers. An offshoot into the ninth later, Nessus, was rumored to run through its trenches, but it was unknown how to get here, or if it truly existed at all. Some branches of the Styx flowed down holes in the first layer of the Abyss (which were conduits to the various levels) and some of these holes supplied water to the Styx in reverse waterfalls. Vortices in the river linked to the Elemental Plane of Water. The Styx did not extend into the Astral Plane but portals existed along its banks. It was theorized by some that the ice of Ocanthus in Acheron was either the destination or the source of the Styx, and that the lost memories remained here, trapped in the ice.

The World Tree cosmology model renamed, relocated, and reorganized the lower planes into the Fiendish Planes and the Styx was referred to as the River of Blood.

In the World Axis cosmology model, after the Spellplague, the River of Blood/Styx flowed through the Abyss and the Nine Hells before dumping its pollution into the Astral Sea.

Description
The river was a deep, swift torrent that could not be forded.

Described as dark and foreboding, the water was greasy and foul, covered in bubbles and debris, while its banks were lined with the rotting remnants of battles fought there.

Powers
Just a touch or taste of the water was enough to give one complete amnesia and act as if under a feeblemind spell if they lacked the fortitude to resist. Even those who did withstand it still lost all short-term memory of the previous eight hours. A spellcaster would keep their prepared spells in mind, but might forget they had them.

Inhabitants
Travelers were advised to use the boatman Charon or his servants (the charonadaemons) to navigate the river. As well as these fiends, some ferrymen and ferrywomen were petitioners (spirits of the dead) or a rare mortal. Whatever they were, these sinister ferrymen were adept in navigating the chaotic currents and eddies. They were willing to take travelers between the planes, but for a price.

If nonnatives attempted to circumvent the river by flying or walking over it, there was a good chance of attracting hydrodaemons or styx devils.

The Styx's headwaters were located in the plane of Pandemonium. There, its deleterious effects were not as powerful as in other layers, so merely touching the water or the spray produced by the plane's intense winds caused no ill effect. While every bit as chaotic and unpredictable as in other planes, the branches of the Styx in Pandemonium were usually shallower.

Rumors & Legends
The silt at the bottom of the Styx was rumored to contain the memories of all the souls who had lost their identities to the river. The shadar-kai were always interested in obtaining the material from adventurers, who sometimes sought to collect vials of the sediment in order to offer it to the Raven Queen in exchange for a boon or divine favor.

Inhabitants
The shallow headwaters of the Styx were inhabited by large versions of freshwater wildlife, such as quippers, eels, lampreys, snails, and crustaceans. The river was also inhabited by Styx dragons, who tended to build lairs along its banks.

Appearances

 * Adventures:
 * The Rise of Tiamat