The Demiplane of Shadows

The Demiplane of Shadows, (also known as the Twilit World, Shadow World, and the Place of Shades), floats between the edges of the Material Plane and Shadowfell. Much of the terrain takes in elements of both, taking in settlements as well as mountains, plains, seas, and other natural features. Each part is exceedingly dull, comprising of darkened shadows, gray skies (ranging from light to dark), and a barely noticeable sun during the dark daytime. The shadows cast by any light source extends further than normal, and like the Shadowfell, appear dimmer & with little warmth. There is always the feeling of being watched and of movement in the dark corners of this Plane. Water and food appear to give little sustenance here, and appears dull & muted in taste & smell. Any colour that appears fades with time to a white, gray, or black colour in time, though if brought from another Plane, will quickly revert back when taken out. Like many worlds life does exist here, but appears bleak, and almost lifeless at first. Most creatures seem to exist here in some form except for a small specialised groups. Those that do tend to belong to the Material Plane, with the exception of dragons and undead. It seems to be hostile to these forms, yet other creatures exist that more than make up for it.
A strange type of life exists in the Demiplane. Beings born of pure shadow live here, each appearing to mimic other life yet are wholly different. Shadow wolves live in many regions, feeding on prey like real wolves do and hunting in packs. Snakes appear also in shadow form, slithering through the shadows feeding on other animals as well. Creatures similar to large or bigger predatory birds are sometimes encountered, again preying on other creatures. There are many such animal-like shadow creatures, all predatory in nature, yet comprised of pure shadow. The strangest though, are the shadow people. The majority are humanoids, tall & thin, along with featureless features, long coats or cloaks billowing out from them, and many with wide brimmed hats, they stalk the land and the living. Some seem curious about living humans and humanoids, others hostile and threatening. A deep discomfort to outright horror surround them. They don't seem to eat, drink, or sleep, and latch onto a living person or area, and suspected of feeding on fear or terror. They never seem to directly interact with the living, yet can still move inanimate objects at will. Sometimes, their eyes appear to glow when seen, and usually are encountered just before or after sleep.
There is one being though that seems to terrify all others here. A tall slenderly-built creature dressed in a white shirt, and other black clothes stalks the land. Having a bald, featureless head, it can sprout tentacles out of it's back at will. It feeds on anyone or anything it can, including other shadows. Thought to inhabit a building somewhere in a darkened shadowy city, it strikes out regularly to hunt. Always alone it is rumoured to have reduced the city it regularly dwells in to a lifeless shell of past glory, with all matter of treasure & magic still intact.
Exactly how this plane, and the shadowy creatures that appear on it, came to be is somewhat of a mystery. A few sages studying this, point to a time when the Shadowfell, and the Dark Gods that govern aspects of it, were at war. They were embroiled in conflict with a  group referred to as the Heavenly Host. This Host seemed to look to bring light to darkness, and prevent the Shadowfell gaining traction in other planes. The latter had set out to corrupt as much as they could through the use of a set of warlocks. These warlocks were due to carry out a grand conjuration across many worlds using a set of collected spells called the Grand Shadow Grimoire, a powerful Book of Shadows containing distilled knowledge of the masters of the Shadowfell. If the book could be stolen away and/or destroyed, then the conjuration. The Heavenly Host was successful, casting down the Dark God who led the Shadowfell ensemble, and spirited away the book. By doing so, they prevented it happening, though a counter attack caused the book to be lost. At this point, a new demiplane appeared, at the same time, and now rumoured to have both the god, and the book at it's centre.
The local people are primarily Human and Halfling, with small amounts of Elves, Dwarves, Gnomes, and Tieflings. Most are farmers, traders, militia, and other types of day-to-day jobs are carried out. None of the people seem to get any real enjoyment out of working let alone living here. Suicide and depression is quite high amongst the people too. Most live near or in settlements of different sizes ranging from villages up to cities. Most large towns & cities are made of granite or basalt, with wood being another major building material. The granite, basalt, and wood used, are dull and lacking any real colour, usually appearing the regular tones of gray encountered elsewhere. Most of the citizens hear of a city at the centre of the demiplane surrounded by stout walls of granite & basalt, with no guards or travellers coming or going. No smoke from fireplaces, or animals seem to be anywhere in or around it too. They say a great evil lurks in the castle at the centre, ruling the lands around, stalking and killing any who gets too close. Each has heard of a few brave outlanders, who appear at random in the demiplane, travel into the city never to be seen again. Sometimes a scream can be heard on the wind before fading again. Most of these outlanders simply vanish, and a good few in the city, trying to find out about why they ended up in this cursed land. That and the rumours of the vast treasures that can be found there, especially the castle's treasures, one of which appear to be a magnificent ancient tome of magic sealed away below it.
Sometimes the demiplane encroaches on other realms. The Shadowfell regularly touches it allowing living creatures to pass from one to the other. The Material Plane, especially with populated worlds also seem to be regularly touched too. In the latter instance, a number of disappearances of individuals have been ascribed to this happening. Also, with the appearances of shadow people in certain areas, there appears to be some kind of further interaction as yet unknown happening. On another note, there seems to be a number of doorways rumoured to be in the as yet unnamed city leading to other demiplanes linked to the Shadowfell. A rare few people in the demiplane refer to the city as Unknown Kadath. The reason has never been noted, and the person regularly has no explanation as to why they refer to the city as that.

Geography

The demiplane is surrounded by an endless ocean, with coasts made up of beaches of sand or rocks, rocky outcrops, or swamp/mangrove inlets. Plains, forests, rivers & lakes, swamps, and hills all are found inland with the very centre being a mountain range stretching high up into the clouds. Roads surrounded by forests penetrate the mountains and at the centre is a valley where a city lies abandoned and dead. Small villages & towns are found regularly around the different biomes with farms attached.

Ecosystem Cycles

There appears to be no late Spring, Summer, or early Autumn. This in part is due to this period being only slightly warmer and drier, with slightly less cloud, than the rest of the year. Other than that, it follows the patterns of most worlds, with the winter being especially bad compared to others. Also, less snow fall occurs but having higher levels of rain and sleet instead.

Localized Phenomena

The demiplane is in constant low light, covered in clouds of different thickness, and seems to have very little colour. Most colours seem to be made of gray, with slight tinges of other colours coming through. Shadows abound here, and seem almost sentient. Depression and miserable feelings are common occurrences here, along with suicide.

History

Millions of years ago, a Heavenly Host attacked the Dark Gods that are tied to the Shadowfell. They were preventing a catastrophic spell being released from a book called the Grand Shadow Grimoire. They succeeded in dispersing the Dark Gods alliance and the warlocks who had received the grimoire. By doing so, they damaged the Shadowfell, casting the leader of the alliance into a new dimension. This dimension became the Demiplane of Shadow. A portion of the Shadowfell's essence was imbued within the demiplane. The dark god that was banished here still exists somewhere around an ancient city, and from there started to create new life, as well as draw creatures, intelligent life, and plants into the demiplane. Here, he feed on the inhabitants body & soul, creating his own children when glutted on the souls he ate. These led to the first shadow people, and with the leftover residues created shadow animals.
The dark god keeps the borders of the demiplane accessible to the Shadowfell and the Material Plane, where it sometimes touches. All through this time many Humans & Humanoids have travelled to this dreary place. Nany seek the treasure or the grimoire, others for adventure, and a number looking to target & prevent the shadow people crossing over. On many worlds there are tales of these beings affecting places in negative ways, sometimes bringing with them a part of the demiplane. The dark god rarely leaves, though does so when feeling especially hungry. He does this rarely though as if he does not return then he is obliterated, as no other dimension can tolerate his presence for long. This is part of his curse, nut can spark legends on other worlds leading a few to worship him, and others to seek him out.
The Shadowfell prevents any incursion from here, having done so since the initial sundering of the lands. Shadow people and the god is not welcome anymore in their lands, and the undead are unwelcome in the demiplane too. This in part is due to many undead being essentially soulless, making it a pain for the god to feed. Many purges have took place of the millennia to wipe out groups of undead, such as vampires and mummies, due to this.

Type

Dimensional plane