Styx

The Styx, also known as the River or Blood, was a cross-planar river that linked the topmost layers of the Lower Planes according to the Great Wheel cosmology, and all of the Fiendish planes according to the World Tree cosmology. Those who touched or drank from the Styx would forget their past lives completely for a while, sometimes permanently.

Great Wheel
The Styx crawled through the uppermost layers of the seven lower planes, as described by the Great Wheel cosmology model: Pandemonium, the Abyss, Carceri, Hades, Gehenna, the Nine Hells, and Acheron.

Its headwaters were located in Pandesmos, the uppermost layer of Pandemonium, as well as several of the river's tributaries. There, its deleterious effects were not as powerful as in other planes, 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.

In the Abyss, the Styx wound around the Plain of Infinite Portals, the first layer; some channels poured into pits, bringing its waters to some of the deeper layers, while foul water welled up out of other pits to rejoin the Styx. In the layer of Thanatos, the river fed a moat around Orcus's palace of Naratyr. In the layer of Shedaklah, the Styx separated the regions under control of Zuggtmoy and Juiblex.

In Orthrys in Carceri, the river mingled with the canals and bogs and soaked the ground with its magic. Unlike in other planes, merrenoloths asked for a much lower price to ferry passengers into Carceri, but charged an exorbitant fee of 5000 gp to ferry a passenger out of the prison layer.

In the Khalas layer of 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.

In 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 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. A little known offshoot ran through the trenches of the ninth later, Nessus, into a pool known as the Forgotten Lake. However, it was unknown how to get here, and some said the branch did not exist at all.

In Avalas, the top layer of Acheron, the Styx would emerge from a crater on one cube, run for miles, drain down into another crater, and reappear on a different cube entirely. Sometimes, it changed course and drowned whole cities, taking with it memories and lives. 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.

One particular cube in Avalas allowed for unusual predictability in the river's course. The Styx ran perfectly uniformly on all six sides of the cube of Wreychtmirk, and flowed from each of those sides into a specific Lower Plane. Each face of Wreychtmirk assumed the characteristics of the destination plane, so a passenger always knew where to end up when embarking from any of the cube's faces.

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.

World Tree
According to the World Tree cosmology model, the Styx was referred to as the River of Blood. The huge and stinking river flowed through many of the Fiendish planes, connecting them similarly to how the World Tree connected the Celestial planes.

The source of the River of Blood was thought to lie somewhere in the Abyss. The river ran strongest through the Abyss, Blood Rift, and the Nine Hells. It also wound its way through the Barrens of Doom and Despair, Clangor, Fury's Heart, Hammergrim, and Nishrek, and ultimately poured out into the Fated Depths. The only fiendish planes not connected by the River of Blood were the Supreme Throne and the Demonweb Pits.

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

Geography
The river was a deep, swift torrent that could not be forded. Its surface moved slowly and sluggishly, hiding a dangerous subsurface current that could quickly pull boats and swimmers to the bottom.

The water flowing on the Styx had a foreboding dark color resembling dark wine that constantly exuded a putrid odor. It was oily, greasy and foul, covered in bubbles and debris. Its banks were lined with the rotting remnants of battles fought there.

Powers
Despite its uninviting appearance, the waters of the River Styx were still a temptation to thirsty travelers in the Lower Planes. However, just a touch or taste of the water was enough to inflict complete amnesia and an effect similar to a feeblemind spell upon a drinker unable to resist it. Even those who did withstand it still lost all short-term memory of the previous eight hours. A spellcaster would keep prepared spells in mind, but might forget about having had them in the first place.

The only fiends known to be completely immune to the deleterious effects of the Styx were amnizus, hydroloths, and merrenoloths.

History
The Styx was the backbone of the Blood War. Its banks were potential battlegrounds in any plane they touched. In particular, demons entered Avernus by navigating the Styx from the Abyss.

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.

Travelers were advised to use the boatman Charon or his servants, the merrenoloths, to navigate the river. As well as these fiends, some ferrymen and ferrywomen were petitioners or, rarely, mortals. 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. When traversed by competent navigators, any point along the banks of the Styx could be reached within a day.

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

Appearances

 * Adventures
 * The Rise of Tiamat