Inhabitants of Shadowfell

Riven stood in the uppermost room of the central tower of his citadel — a fortress of shadows and dark stone carved in relief into the sheer face of a jagged peak. . . . The starless black vault of the plane’s sky hung over a landscape of gray and black, where lived the dark simulacra of actual things. Shadows and wraiths and specters and ghosts and other undead hung in the air around the citadel, or prowled the foothills and plains near it, so numerous their glowing eyes looked like swarms of fireflies. He felt the darkness in everything he could see, felt it as an extension of himself, and the feeling made him too big by half.

— Paul S. Kemp, The Godborn

The Shadowfell is the the dark reflection of the physical, a dimension of black, grey and white, where most other colours just don't exist. It is a place of darkness that hates the light, where the sky is a black vault with neither sun nor stars. It appears similar to the phyiscal world without colour, but are twisted and warped, a distorted vision of the material plane.
Many creatures exist on the plane, undead, orcs, Fae and Shadow Elves all make they homes on this bleakest of planes.

Court of Shadow Fae

Like the Light Court, the shadow is made up of Eladrin Fae in the main, darker and more brooding than their light cousins. Along with the Archfae, the Lords and Ladies of the Court, who take many forms from shadows to dark and brooding elves. Above the Ladies and Lords are the Queens and King of the Shadow Court. The 3 Queens, the Winter Crone, Queen and Lady, who all beyond the comprehensive of the mortals of the physical plane, along with the King Oberon the King of the Shadowry Forests and dark corners.

Elves of the Shadow Court

The Elves of the Shadow Court that still live in the shadowfell are very similar to those in the material. They no worst than those of the court of light, they not evil just selfcentre like all Fae creatures. Yes they tend to wear darker colours and tend to treat lesser mortals as nothing but hell when you live a thousand years those that live 80 seem insignificant to you.

Orcs

The Orcs of the Shadowfell are creatures of the dark and are creatures of vicious temperment they have to fight every second of the life to stay alive in the bleakness of the shadow plane.

Lesser Fae

Hags, Pixies, Sprites, Succebus and Incubus are in the main members of the shadow court, most live in the towns of the Fae and Elves. But a few do still hold their independances from the greater Fae and dig out a live for themselves out of the sight of the courts. A few manage to find they way into the Material plane, and gain power via offering deals to mortal beings on Godai.