Shadowfell

The Plane of Shadows
"It is the toxic plane of darkness and power. It is the hidden place that hates the light. It is the frontier of worlds unknown."

If the FeyWilds is the echo of the Prime Plane, then Shadowfell is, well, it's shadow. A dark and twisted landscape shaped by twisted wants, desires and despairs. This land feels empty - there is never wind, the water has no crashing waves. It's stillness can drive a man crazy within minutes due to how wrong it feels. Madness seems to be a common theme in those who get trapped in the Shadowfell. When it rains, the sound of raindrops is muffled. There is no thunder, no flashes of lightning. Being the Shadow of the Prime Realm, the Shadowfell takes what exists and darkens and twists it. A home in the Prime realm is a rotting structure in the Shadowfell, with tendrils of vines voering it. A living forest in the Prime realm is a forest of dead trees, ash covering the ground. Sometimes ash falls from the sky as if a distance volcano erupted. Riverbeds are dried out, cities are nothing more than ruins of rot, decay and gravity taking its toll. Standing stone structures like castles and forts still stand, but they are dusty, dark places, and anything inside has started to rot away as well. Light doesn't seem to travel far, as if this plane absorbs it quickly, sucking away the light.

These twisted lands also seem to never have sunlight, only a pale glow from the clouds, enough to make the land have a dim light if not obstructed. Those who wander around the Shadowfell for 5 days may end up with some slight curse, and every five days thereafter, the curse worsens if they are cursed, or they may be cursed again.

Inhabitants
"How could anything survive in that land, let alone be content with living there? Any regular mortal would be driven mad..."

The Krinth
Once a slave warrior race, the Krinth are low in number but do reside within Shadowfell. They have refuge within the ground in some places, making settlements out of the stone. However, not much is known about them or their society or how they interact with outsiders. Said to be the offspring of demons, the Krinth are hideously malevolent in appearance. They were tall humanoids with dusky gray skin, black hair, and black eyes.[1][2] They weighed between 150 and 250 pounds (70 and 110 kilograms) and were between five and seven feet (150 and 210 centimeters) tall. They are known to not understand humor and may come off and short tempered and grumpy. They have no sense of metaphor or poetry. They abject lack of extreme emotion protects them from being turned mad.

Shadar-Kai
Once upon a time, the Shadar-Kai were elves that followed the Raven Queen. They gave up their life force for their Raven Queen to become more and more powerful as she attempted to become a deity. However, everything went wrong, and they were cursed to live in the Shadowfell for the rest of eternity with the Raven Queen as their guide. The Shadar-Kai have very reckless natures because, if they die, they know their Queen will reincarnate them back in the Shadowfell as she now has almost godlike powers in this plane. It is her madness that drives those trapped here mad. Shadar-Kai almost exist in a state between life and death, looking blighted with pale skin and dry lips, but their eyes are wild. When outside of Shadowfell, they show visible signs of rapid aging, and will wear masks to cover up their aged features. Each Shadar-Kai wants to live life hedonistically and to the ultimate pleasure, seeking thrilling experiences to feel alive and stave off the aging effects.

THE RAVEN QUEEN'S MATERNAL NATURE
The Raven Queen long ago was an elf queen who sought to help end the conflict between two warring deities by rallying her followers to give herself enough power to become a deity herself. To do this, her followers offered their souls and magic because they believed strongly in her and her cause. These followers would later become the Shadar-Kai known today.

The Raven Queen was well on her way to accomplish her task until evil wizards that entered the ranks of her follower unbeknownst to her corrupted the ceremony in an attempt to steal some of the power she was gaining. She discovered this, however, and her backlash caused those evil wizards, herself and her followers to be dragged into Shadowfell because the ceremony corrupted their existence. The Raven Queen fell first, and her entrance and corrupted state shattered her, causing her an instant death. However, her essence was spread throughout Shadowfell, and her consciousness - now shattered and mad - rules over the plane, sometimes materializing in the form of ravens coalesced into a human image.

Her followers became the Shadar-Kai, and those evil wizards were twisted and shaped into Nagpas - evil entities cursed to walk Shadowfell forever in a corrupted, insane state.

The gods erased the knowledge of her from all elves outside of Shadowfell, but her power allowed her to maintain her memory in her followers. She then gathered the memories and created the Fortress of Memories, and then sought to collect memories from those on other planes too in order to sustain her and her essence.

However, her madness and the tainted essence of Shadowfell blended together, bestowing curses upon those who are trapped in this land from other planes. These become the Sorrowsworn, so twisted by the negative aspects and emotions of one's self that they become a physical embodiment of their sorrow. The Wretched, The Lost, The Hungry, The Angry, and The Lonely. They all also represent how the Raven Queen feels at the betrayal of those who were supposed to help her end the war and do good for the world, and towards those deities that tried to erase the memory of her from existence.

In Vorel Vur Korth's Shadowfell mirror, the Raven Queen's maternal nature is dominant. She cares for those that have been born or touched by the Shadowfell, and she is less deadly here than other regions where her madness still runs wild. However, the Sorrowsworn are still a threat, as well as other threats throughout, because the Madness of a Mother is powerful and intense.