Leviathan
The darkest chants suggest that Leviathan was once a spinal leech, one of the baatezu-engineered parasitical worms, implanted in a spinagon experimentally. Somehow, he became sentient, and began to take over. He envies those born baatezu, and to try to *become* them he invented the spinal leech, a small piece of himself he uses to control others.
Ultimately, he wants to become all of the multiverse.
Leviathan is responsible for many atrocities, including slaying the former queen of the eladrin, and slaying Bensozia, the Queen of Baator herself. In both cases he replaced them with mind-wiped slaves and attempted to pass them off as the originals. In both cases he failed, but he's learning. On the Prime Material, Leviathan enjoys infiltrating large governments wilth similar slaves and secretly manipulating whole nations. World leaders kiss his ring and call him God.
Leviathan's servants are collectively called the Lotanites, and they include the abhorrent amnizu as well as a number of odious nobles who do what their master cannot in his icy prison. Exirion is the Chief Justice of Leviathan, a great mound of chiton with multiple arms and eyes who judges alleged crimes against Prince Levistus from its icy throne. Amon the Wolf remained loyal to Geryon, but the amnizu are diligently attempting to convince him to betray his master. Dagon is the Warden of the Stygian Depths, responsible for the defense of the undersea realms. They say Dagon was once herald for Adramalech until he was banished for selling the secret names of baatezu nobles; only with Levistus' reinstatement was he able to regain an official position in Hell. Dagon has proved his worth to Levistus many times over. The amnizu act as spies for Leviathan throughout the run of the River Styx through Baator, and they rule malicious courts of sniggering abishai and other lesser devils, holding trials for trespassers.
The Hand and Voice of Levistus are the gelugon spell-hurler Erridon Alaka and Zanth, Eater of Innocents. Zanth is Erridon's son by a mortal concubine; their hellcat is Trinity. They were recruited from the Loyalist faction to stand above the petty bickering of the City of Ice. Erridon Alaka is Levistus' enforcer and assassin in the city, while his half-mortal by-blow speaks for both his sire and his lord. Zanth has a half-dozen ice stalkers with him at all times, busily fetching mortal children for him to eat.
On occasion Leviathan has manifested an avatar or projected image of a darkly handsome, brooding man with reptillian skin and icesickle spines. His psionic powers are said to be incalculable.
Priests of Leviathan gain their spells from the sahuagin god Sekolah. This situation may change, however. Levistus' war against Set has come to an uneasy peace since the lord assigned two of his nobles, Krotep and Nekhet, to the Heliopolitan god's realm, while Dagon's fondness for Material Plane worshippers from the sahuaghin race has caused relations with Sekolah to sour.
STYGIA
Stygia is the chill sense of eternal forgetting, the great infinite sea of Hell. "Amnesia is suffering," say its inhabitants. "Suffer, then, and glory in it."
The Styx is more ancient than any of the lower planes, says Levistus, and its greatest flow is in Stygia. The agony of loss personified by the Dark River is the ultimate power, and it is dishonorable to serve any lesser law. Betrayal, then, is in accordance with this greater law, and it should be encouraged. In this way this most eternal order shall devour the other circles of Hell.
Stygia is mostly made up of the wine-dark pollution of the River Styx, which reaches unfathomed depths of bitter cold and foulness. On the surface, it becomes enormous ice floes as treacherous and clashing as the inhabitants of the layer. In the sky are terrible storms, as if lost memories become etched across the sky in lightning. Beneath, strange things lurk. Some claim that the layer was once dry, but it was flooded in order to drown forever the secrets of the plane in watery oblivion.
The city of Tantlin is built on an iceberg with a natural harbor. Its pit fiend ruler, who has willingly sacrificed its name and past to the Styx in exchange for power, constantly manipulates the cities various factions against one another, allowing their conflicts to erupt frequently into violence. It knows that all loyalties must be forgotten in order to prepare the servants of Levistus for their upcoming roles. Most of the leaders of Tantlin are amnizu, but a few are cornugons, gelugons, and paeliryons.
The baatezu caste most identified with Stygia are the bone devils, the osyluths. In part, this is due to confusion with the bonedregs, those skeletons frozen in Levistus' ice and released, animated with soulstuff and sent to do the bidding of the Prince. However, an unusual number of true osyluths dwell here, sent by the Dark Eight to carefully watch the populace for signs of disloyalty. Due to the machinations of the amnizu, these signs appear with frequency. Glass devils are another frequently seen caste, their transparent forms enabling them to blend in with the ice. Ice stalkers are sometimes reported, though whether they spy for Levistus or Molikroth of Cania is unclear.
The xerfilstyx baatezu were once the prize minions of Geryon, Stygia's former lord, created in his own image. When Geryon was cast down and Levistus reawakened, the Prince of Oblivion cast them into the Styx (and banished most of them to Avernus), where they went mad. A few wander the ice and water of Stygia still, forgetful as they are of the origin of their pain.
Some also still serve Geryon, who lives now in his Citadel Coldsteel. There he broods with his minotaur worshippers and thinks of vengence, but mostly he still does the bidding of the Dark Lord of Nessus, who holds the key to his restoration. Doing his bidding is the wolf-headed duke Amon, though some claim that Amon is not as loyal as he seems, and serves Levistus in certain matters as well.
Beneath the ice is the realm of the sahuagin deities. Sekolah is a multi-aspected being, both savage predator and sly, patient tutor, father and mother and greatest nemesis of the sahuagin race. With its sea devil minions the shark-god devours the lost souls that drift aimlessly through the waters of the underworld, and also hunt the squid-god that the sahuagin worship as the incarnation of all prey. Some theologians suggest the squid has a sea-elf aspect and a connection to the zoveri of Mount Celestia.
Sekolah feels nothing but hatred for Levistus' loyal servant Dagon, who steals sahuagins and other aquatic creatures and breeds them with devils to create his aquatic army. Halfbreed hamatula/sharks are as common as erinyes/aboleth and barbazu/orcas. Dagon also upsets the various watery Abyssal lords by sending some of his half-fiendish creations to the Material Plane to create cults among races such as the ixitxachitl and the kopru. Once, Dagon was Jaqon, a servant of the Lord of Nessus in charge of remembering the true names of all baatezu. Jaqon abused his position by selling these names to mortal and yugoloth summoners, so in punishment Jaqon lost his own name and his position too. After living as an exile in Avernus for milennia, Jaqon (now renamed Dagon) was allowed to return to duty in a particularly ironic way. After serving as a patron of memory, now Dagon would dwell in the waters of forgetfulness as a submarine servant of the newly reawakened Prince Levistus. Surprising his former associates, Dagon took to this role like a fish to water. He wouldn't go back if he could.
The Hand and Voice of Levistus are the gelugon spell-hurler Erridon Alaka and Zanth, Eater of Innocents. Zanth is Erridon's son by a mortal concubine; their hellcat is Trinity. They were recruited from the Loyalist faction to stand above the petty bickering of the City of Ice. Erridon Alaka is Levistus' enforcer and assassin in the city, while his half-mortal by-blow speaks for both his sire and his lord. When Zanth speaks to the inhabitants of Stygia, they listen, for his words carry the weight of Levistus himself.
Zanth, the Rape of Innocence, is a half-gelugon, significantly taller than the human slave that sired him with insectoid eyes and mandibles growing out of the sides of his attractive human face. His body is mostly covered in chiton. The hunched, skull-faced ice stalkers that follow him like dogs are, he is certain, clean of the taint of their creator Molikroth. They fetch mortal children for him to eat, and if they report to Cania he is not aware of it.
Trinity, some speculate, is the real power of the group, responsible for ensuring its companions' obedience to its infernal master. It resembles Levistus itself in its lack of either useable hands or voice, but its silence is a mark of its efficiency. In darkness the bezekira can be seen as a faint glowing haze following Erridon Alaka about its tasks or keeping a watchful eye on Zanth's pack of ice stalkers for signs of treachery. Once it was an amnizu, and why it was condemned to this faster, more feral form is a mystery. Trinity says nothing. The common explanation of its name (that Trinity, the Eye and Ear of Levistus, forms a trio with the Hand and Voice) is seen as incomplete by many. Some say the real trinity is the hellcat, Levistus himself, and one other who remains unknown to any outside the group, or refers to three forms the bezekira can take.
Ankhwugat, the Hours of the Night, is the realm of Set. Set is the dark master of the desert, lord of serpents, jackals, assassins, and creatures of the wild. Though dark waters flow underneath his realm, its surface is hot and dry as the sands of Pelion, and those familiar with the realm of Nephythys there will see Ankhwugat as a twisted reflection of that one. When Set and Nephythys divorced, Set went to Stygia to forget his pain. Perhaps once all Stygia was like Ankhwugat, and perhaps, if Set has his way, it will be again. Some claim that Set is mad and wishes to transform the layer or even turn his realm into a new outer plane set between Baator and Acheron. Others say he only wishes to reunite with his estranged wife Nephythys, and that the mad ones are the baatezu who try to earn his favor. The common chant says that Set and Levistus are headed toward a showdown. The will of a Lord of the Nine is supposed to be absolute in his layer, but Set has the good will of Ra and Levistus is imprisoned in ice.
In the cold outside, two baatezu nobles guard the borders of the realm. Krotep and Nekhet both petition the dry god for recognition with increasingly extravagant and dangerous gifts, gifts that perhaps mirror the ones that Set himself sends to Nephythys, but their only answer is the howl of the desert wind.
Factions of Tantlin:
The Loyalists are fanatically dedicated to Levistus. Led by a cornugon (Mattex), they are an old faction, having existed even when Geryon was Lord of the Fifth. They have lost some of their fervor since their hero's reawakening, but have the assistance of most of the amnizu in fighting off attacks from rival factions. Thus, their war is primarily a defensive one.
The Royalists believe that Levistus is not imprisoned in the ice at all. Contrary to the common story, they do not believe that Levistus was imprisoned as punishment for slaying Queen Bensozia of Nessus. Instead, they insist that Levistus was imprisoned for some prior crime, and he instead somehow switched places with the Queen, leaving her entrapped in his stead. The Royalists believe if they take over Tantlin, they will be able to set the Queen free. They are led by a paeliryon called Ingraine.
The Horns of the Beast are loyalists of Geryon. They hope to reconquer Tantlin for the fallen lord. Many of them were previously loyalists of Levistus, and switched sides once the Devourer of Memories regained power. Their most vocal advocate is a barbazu warrior called Cryon.
The Seekers of Anamnesis wish to depose the nameless pit fiend who rules Tantlin. They believe they can do this by recovering the pit fiend's name. It has been lost in the Styx, and the pit fiend has evaded attempts to slip desert's night blossom into his food through the use of imp food tasters, so they intend to learn the fiend's name from Dagon. Dagon was once in charge of knowing all baatezu truenames, and due to a boon from Levistus (or the Dark Lord of Nessus), he is himself immune to the Styx's memory-draining effects. Thus far, Dagon has been silent. The Seekers try to coerce him by attacking his followers and his rarely-visited home in Tantlin. The Seekers are led by a gelugon who hopes to replace the pit fiend after giving his own name to the waters.
The Antediluvians believe in a Stygia that existed before it was flooded netherworld waters. They hope to bring that Stygia back by sacrificing victims to the floods. With the aid of fresh souls and dire rituals, they believe the Styx will be appeased. They are led by an amnizu called Pelagon.
The Bringers of Eternity, in contrast, hope to flood all of Tantlin with Stygian waters in order to cleanse it. The amnizu Archiphlax hopes to convince the waters to rise by sacrificing memories to it, while the hamatula Doe is trying to melt the iceberg by converting the locals to the worship of Lady Fierna.
The Stygian Puritans believe that all uncertainty is chaotic and affront to Baator. They mostly spend their time harassing the gamblers who congregate on heavily-armed boats in the harbor.
The Icy Breath of Kriesha are followers of the Vos goddess of winter, whose realm is in Stygia. From a frost-covered temple they seek to expand the influence of ice by freezing the rest of the layer. They are equipped with powerful magics by their goddess, and if it were not for the efforts of the amnizu and the Bringers of Eternity they might well have accomplished something by now. Why Levistus permits their existence is a mystery, but doubtless has something to do with the complicated treaties between the gods and lords of Hell.