Adding Color to the Grey Wastes

Speaking of Nyx and the Cacodemons, you might be interested in the whole Protogenoi history I've been working on in the timeline topic. The Protogenoi were the race of gods who preceeded the Titans, and include Nyx, Erebus, Gaea, and Uranus (Gaea is actually a Protogenai, not a Titan). If you're interested, you can read about it on theoi.com. Since Protogenoi is a generic enough term (meens "first generation" in Latin), I've also included the Ogdad and deities from other pantheons in that list (including Chauntea, Selune, and Shar, as well as the Elemental Lords of the Faerunian pantheon).
As per their description in Greco-Roman mythology and Egyptian mythology, the Protogenoi were originally elemental beings, though some of the still-remaining ones have since changed form. They were formed on the Inner Planes, and NOT the Outer Planes or Astral (unlike the Titans and later generations of powers). Eventually, most of them moved to the *at the time* still unformed Outer Planes after discovering the newly-formed Astral. However, the Outer Planes and Astral were the dominion of the Draeden, a species of planet-sized aberration left over from the previous creation cycle *the Draeden came to be when the previous multiverse was around 75~80% destroyed* It was the Protogenoi who went to war with the Draeden early in the Multiverse's history. This occurred before the birth of any mortal race, including the Aboleth, and IIRC, before the Yugoloths were even born. The war was ultimately a draw, with the Draeden deciding to go into a state of hibernation until the gods simply disappear. This process was slow and many of the Draeden didn't go into their slumber immediately.

Nyx and Erebus initially sided with the Draeden (not wanting matter to be created), but switched back to the side of their kin when the Draeden reacted to offer with violence.

The Protogenoi I have listed thus far are:
--Aether: The second-generation protogenos of light. He is the son of Nyx and Erebus.
--Akadi: The Elemental Lady of Air.
--Amun/Amaunet: One of the hermaphroditic Ogdoad, and Protogenos of creation and secrets. After suffering severe injuries in the Draeden War, he went on to become the Egyptian solar power Ra.
--Ananake: A protogena of innevitability and eternity. She is the mate of Chronus.
--Beory: The earth Protogena of Oerth.
--Chauntea: The earth Protogena of Toril
--Chronus: A protogenos of time, not to be confused with the Titan Cronus.
--Eris: A protogena of discord, and the most powerful of Cacodemons (beings unleashed from Pandora's box). She is the virgin daughter of Nyx, borne asexually. Like her mother, she has also borne many children asexually, all of them cacodemons. She is one of the few Cacodemons to ever reach deity status.
--Eros: Aka Eros-Phanes, the protogenos of procreation, not to be confused with the Olympian god of the same name.
--Gaea: The protogena of earth, and mother of the Titans.
--Grumbar: The Elemental Lord of Earth.
--Hemera: The second-generation protogena of day, daughter of Nyx and Erebus.
--Huh/Hauhet: One of the hermaphroditic Ogdoad, and Protogenos of eternity and infinity.
--Hydros: The protogenos of water. During the Draeden war he was sundered in two, into Oceanus and Pontus.
--Istishia: The Elemental Lord of Water.
--Kossuth: The Elemental Lord of Fire.
--Kuk/Kauket: One of the hermaphroditic Ogdoad, and Protogenos of darkness.
--Liga: The first incarnation of Pelor, originally a 2nd generation Protogenos of neutral alignment. Pelor is the fifth incarnation of the deity and probably a split off aspect.
--Lunitari: A third generation protogenoi of one of Krynn's moons.
--Nu/Naunet: One of the hermaphroditic Ogdoad, and Protogenos of primordial water.
--Nuitari: A third generation protogenoi of one of Krynn's moons.
--Nyx/Nox: A protogena of the night. She bore a few protogenoi with her brother Erebus, but also bore many cacodemons asexually. She is also the mother of the yugoloth lord known as Charon, the ferryman of the dead.
--Oceanus: A second-generation protogenos of the sea. He would later side with the Titans against his own people.
--Phanes: A protogenos or protogena of creation and positive energy, who eventually split into several beings, such as Eros, Phusis, and Thesis.
--Pontus: Oceanus's freshwater equivalent.
--Ptah: The protogenos of creation, associated with Amun and Ra, though it is unknown if or when one came before or after the other, or what their exact relationship is.
--Selune: A third-generation protogena of Toril's moon.
--Shar: A third generation protogena of the new moon; she is the twin sister of Selune.
--Solinari: A third generation protogenoi of one of Krynn's moons.
--Tartarus: A protogenos of the dark pit. He was either slain or forced into a dormant state by the Draeden, and the remaining Protogenoi built the prison plane Carceri over his body. Whatever the case, his essence remains intact on that plane and is vaguely aware, though Erebus stole some of his divine power and subsumed his portfolio. (note I think there is something about him in the 2E canon, but I don't recall off-hand)
--Thalassa: A third generation protogena of the sea, daughter of Aether and Hemera.
--Thesis: A protogena of creation, split off from Phanes. She was slain during the Protogenoi-Titan war and her portfolio subsumed by Metis and Tethys.
--Uranus: A protogenos of the heavens/sky. He and Gaea were the progenitors of the Titans.

It should be mentioned that there are two cacodemons which are Olympian rather than Protogenoi-- Phobos and Deimos, the sons of Ares (panic and dread, respectively).

Also, here is a good page for info on the various denizens of the Underworld (the underworld gods are collectively known as the Cthonioi)
http://www.theoi.com/greek-mythology/underworld-gods.html

When I try to think of one word that defines the Gray Waste more than any other, I think 'despair.' Hades is what you get when all hope is stolen from you, when you pass the state of misery and grief and are left with nothing, not even the ability to feel emotion for what you've lost.

That doesn't mean it's a plane with no emotions. There are many steps along the journey to utter Despair, and the plane wrings every torment, agony, and misery that it can from its victims along the way. Victims are left with no emotion only because they've experienced such heights of emotion that there are no more left to feel. It's a deeply sadistic plane, and calling it the plane of sadism is not an exaggeration.

The Gray Waste is a plane that greedily devours identity and everything that makes a sod what they are, including their emotions, but the plane itself isn't unemotional as such; or, at least, it possesses qualities - greed, hunger, envy, loss, sorrow, grief - that might be considered emotions, although they may not be much like human emotions, unleavened by human sentiment or sympathy. The plane exists to create misery, and then to even take misery itself away, leaving barren husks behind.

Some have named the Waste the plane of apathy. This is wrong. Apathy is the excrement left behind after the plane has eaten away at everything else. It's a side-effect, not the goal.

One of the best ways to get down to the core themes of a plane is to examine what happens to souls that arrive there. Most of the dead who come to Hades become larvae. My theory is that all living people have worms of evil twisting through their souls, growing fat on selfishness and sin, slowly devouring more and more of what was virtuous and compassionate until, in some few, nothing but the worm remains, and these mindless worms of evil drop squirming on to the Lower Planes. These larvae may be mindless, but they are still capable of suffering, and in the Gray Waste the night hags and other fiends torment them incessantly until they have no more to give. Unlike other outer planes, Hades also has transparent, wispy soul shades from which even substance has been stolen. For the soulshades, there is no future. Larvae may be incorporated into night hags as part of their reproductive system (they reproduce by devouring larvae) or they may be infected by the plagues and nightmares of the plane, swelling and mutating, any remaining personality traits and sins becoming exaggerated until they become one of the plane's gibbering array of hordlings.

Another way to identify a plane's themes is to examine its natives. There are the greedy, mercantile night hags, thieves of souls and hoarders of larvae. Then there are the baernaloths, the original masters of the plane, who dwelled in the Gray Waste even before it had fully formed. One of their chief abilities is to cause agony in those they encounter, then heal them, and then reopen the wounds in order to make them suffer again and again. This, then, is perhaps the core of the plane.

Disease is definitely a major theme of Oinos. It's certainly described as a place of plague and filth, the festering corpses of the Blood War in no small part contributing to that. Several major gods of disease, Incabulos and Yurtrek, dwell there, tainting the lands around them, but most importantly the station of the Oinoloth and possession of the Siege Malicious grants powers over disease as part of the rights and privileges of office. The master of Khin-Oin becomes "the yugoloth with disease powers."

Greed is an important part of the plane in general. Gods of greed include Hades, Abbathor, Ratri, and Kuraulyek (who stole wings from Syranita).

Death is another theme, as evidenced by the plane's many gods of the dead: Hades, Kelemvor, Arawn, Mictlantecuhtli, Hel. Along with the disease theme, this is probably part of the general themes of misery and the theft of everything that the plane encourages. It's true that every single one of the death-gods I just mentioned tend to be emotionless and either non-evil or barely evil, any passions they might once have had for their job long since drained away. They are left as mere cogs in the machinery of despair, contributing to the suffering without benefiting from it.

This is how I'd sum up the various layers:

Oinos: Disease, war, filth, nightmare, suffering, hoarding. Oinos is infection, horror, pus-filled welts, blood-filled lungs, necrosis. It is suffering for the sake of suffering. It is suffering with no cause. It is suffering with no beginnings; rather than creating its woes, the plane's greatest trick is to strip away everything but suffering, revealing the true agony that always exists and always will exist, on all planes and at all times. It pulls away the curtain and shows reality for the cruel joke it is. Oinos is the heart of the Blood War, transmuting its endless rage into endless, futile monotony. The dark of the Blood War is that it has no heart, and yet where it rages emptily, it rages most of all. There are no reasons for anything on this plane. The plane strips reasons away, and jerks its puppets around in displays of meaningless horror.

Oinos is also the plane of hoarders. Its god Abbathor, its night hags, even Yurtrus with his vaulted realm, protect their gains carefully, not sharing it with prying eyes. This is because they are selfish, of course, but also because they are old and confident. This is the first of the Glooms, and its inhabitants do not feel the need to prove their merit.

Oinos is the first gloom of Hades in more way than one. Not only is it closest to the Astral Plane, but it was the first part of the plane to come into being. It was, sages believe, the first of all lower planes. When the concept of Evil first reified into solid landscapes, Oinos was there, teaching itself what evil might mean. Other lower planes were founded later, either becoming corrupted by Oinos's proximity or founded by immigrants who had begun their lessons on Oinos and spread out to teach new forms of corruption.

But the biggest lesson of Oinos is disease. Disease is how the plane first shows its victims the meaning of despair. There are different lessons further down.

Niflheim: Niflheim, according to the Norse cosmology, is one of the oldest realms in existence, perhaps the oldest. Once Niflheim and its counterpart Muspelheim were all that is. Unlike Oinos, first of the lower planes, Niflheim was not always counted among the planes of evil. Niflheim contained all possibilities, frozen and inert, forever sterile until it came in contact with Muspelheim, which contained the energy and life needed to awaken Niflheim's possibility and turn it into actuality. During the age of creation, when Niflheim and Muspelheim shared the Ginnungagap, the two realms could interact and all other planes and realms formed in between them. Eventually the Ginnungagap grew too full; the World Ash expanded and forced the realms apart, the gods created new realms on other branches of the tree, and Niflheim and Muspelheim were no longer able to create. Niflheim is now once again frozen and dead, its remaining potential frozen forever, sterile and meaningless. Niflheim is now what happens when possibility dies. For this reason it has drifted into the Gray Waste, bonding with Oinos, the first plane of evil, in mutual despair.

Where disease is how despair primarily manifests itself in Oinos, in Niflheim despair manifests as death, and this layer has more realms of the dead than any other. The goddess Shar, who seeks to destroy all life and light and return the universe to the primal void as it was before potential awakened, dwells here as well. Panzuriel, who was once a creator god but now has been cast out, banished and impotent, has been stranded in a slowly dying sea in Niflheim, the sea shrinking as his remaining creative potential is exhausted from disuse. Pyremius, god of fire, poison, and murder, dwells in one of the few remaining remnants of the age of creation, a volcano that had been awakened by Muspelheim's touch but now smokes only because of the divine power Pyremius exhausts in order to sustain it. Niflheim is death created by the loss of power. It is death after all things have become lost or meaningless, sustaining and empowering nothing. It is the layer of loss, and its inhabitants were once more than they are. Even Hel was cast off, Loki's unwanted daughter.

Those who dig deep into Niflheim's frozen possibility might find strange things, creations that might have been but now can never be.

Pluton: Pluton is the third gloom of Hades, and the youngest and most artificial of the three. Where Niflheim is the potential abandoned and cast off after Creation went its own separate way , and Oinos is primal evil itself, Pluton was made by those whose despair resonated with the Waste but who held themselves separate from it. Some say the Greek power Hades built the first of Pluton's realms after he won dominion over the underworld from his brothers, conquering part of the realm of shadowy Erebus and building a palace at its darkest, most distant point, or claiming the kingdom of Nyx for his own. He may not have meant for his underworld to become part of the Gray Waste; it might have been constructed somewhere else, and only slowly drifted toward the plane of despair as its inhabitants lost all hope.

Others point not to the Underworld of Hades, but the mysterious graveyard of the nightmares as the seed from which Pluton grew. No one knows how ancient the nightmare horses, or their now-extinct lords, might be, but there is art depicting yugoloths riding them through the skies in the halls of Khin-Oin, in parts of the tower that long predate the god Hades's rise to power. The lords of the nightmare horses, or perhaps their persecutors, at some point decided that in death the nightmares would at last become free of the domination of others, and a realm was created separate from Oinos, perhaps under the protection of Nyx or under no authority but their own. As more and more nightmares came to add their skeletons to the pile over the eons, the realm around them slowly grew into a realm as potent as either of the Gray Wastes' other glooms. This, then, might be the real theme of Pluton: death leading to power. Certainly this would fit the god Hades' status as one of the young gods of Olympus using a newly-earned mastery over the dead to claim power that wasn't originally his own. Because this is the Gray Waste, the power is built on the bones of countless death, none of whom receive any benefits from it. Still, unlike Niflheim's poor sods, the inhabitants of Pluton tend to be greater than they were. Death has brought them more power, even if they had to give up their individuality to gain it. Even the dead of the Underworld have gained a kind of gruesome splendor in numbers distinct from the piteous, pathetic souls of Niflheim.

Pluton, like other parts of the Waste, is a realm of greed, but where the greed of Oinos is furtively hoarded in hidden vaults or ancient towers, in Pluton it is displayed ostentatiously, like the nouveau rich who have something to prove. Compared to its siblings it is a young plane, and it needs to show its power to the others in order to convince them of its value, despite its comparatively young age. The palace of Hades is a place of dark grandeur, and even the piles of nightmare bones or the city constructed from the still-suffering bodies of petitioners show a need to impress others with tacky magnificence. Piles of bones or cities of bodies may not be 'wealth' as mortals understand it, but in the Lower Planes they're as vulgar as gold, and just as valuable.

Cegilune, queen of hags, also dwells in Pluton. She may be the mother of all night hags, and Pluton may thus be the origin of that race, or she may have been born in Oinos, in the Region of Dreams, or elsewhere and followed the nightmares to ride on the power their bones were forming. She may be a daughter of Nyx, who claimed the primal darkness before the titans were born.

Because Pluton is a young layer, and an artificially created one, the signs of its manufacture are everywhere for those who know how to look. Explorers have noticed that much of the landscape is bound in rings of dark metal or bronze, as if it was deliberately forged.

The torments of Pluton are also artificial. While much of the despair of the other two glooms comes from the landscape itself, in Pluton elaborate punishments are constructed to compensate for the relative lack of native hazards: souls forced to push rocks eternally up hills, food and drink are eternally snatched away from the starving and dehydrated, and other such vulgar entertainments.