The power of Shadesmere has always drawn the ambitious and the striving—sometimes just for a season, long enough to master a few useful secrets—but others have come and stayed. The goddess Satastra is widely acknowledged as She Who Invited the First Visitors, though some claim a more ancient race once made their home in the realm. She brought the shadow fey here, and then the sable elves came, and both of these fey groups brought servitor races.
In the case of the shadow fey, these were shadow goblins, humans, and gnomes. In the case of the sable elves, they were courtfolk halflings, erina, and occasionally alseids, quicksteps, and various sprites and pixies. The land was soon overrun with fey courts and kingdoms in a distant time that both sides refer to as the First Flowering of Shadow.
Beastfolk
Bearfolk. The bearfolk came to shadow not because they were drawn to its power, but because others were. The shadow chewers are said to have first pursued shadow fey into darkness and found their planar bolt-hole. Wise protectors and fear adversaries, the Bearfolk are respected upholders of land and roads.
Ratasok. Guardians of the World Tree, some Ratasok seek the direct source of all shadow-stuff. Some remain steadfast in their mission to combat the shadows wherever they may appear, while others find themselves just as corrupted as other long-time denizens of the plane.
Spiritfarer Erina. Hedgehog-like folk that travel the Shadow Roads. Often they act as guides to other races, burrowing secret roads and mapping the trecherous tides as best they can.
Sublime Ravenfolk. A secretive sect of ravenfolk drawn by mysteris of the shadow and a strange, psychic song.
Weres. Whether cursed or blessed, many find themselves burdened with an animal form. Many forms of weres exist, with just as many origins. Discuss with DM if you would like your PC to be a were.
Scáthesidhe (Shadow Fey)
Scátheside. Almost all fey of Shadesmere are exiles of the Summer Court of the Bright Land fey. Interchangeably called fey and elves, these cunning lords of the land consider themselves the true masters of Shadesmere. They delight in many things, often creatures of trickery, mystery, and secrets.
Lunar Elves. Shadow fey born on rare full moons within Shadesmere seem to be blessed by the celestial body. Their births are considered auspacious events by the communities that house them.
Sable Elves. Where the majority of elves embraced the Shadows of their new home, the Sable elves attempted to flee. Though this was an unsuccessful venture, the ancestors of these first elves have been marked by the attempt. They cling to ancient elven magics lost to their kin and are considered exiles amongst the Shadow fey.
Dusk Goblins. Once servents to 'greater' fey, many dusk goblins have broken free of their old masters and established their own communities. Almost more at home in the shadows than any other race, the Dusk Goblins are numerous yet secretive.
Formorians. Once the most beautiful of creatures, these grotesque giant-kin have been twisted by an anient curse that very few remember. Long ago they fled to the Shadesmere where they have built labyrinthe kingdoms of magic.
Quickstep. Small, quick fey, these mischevious pucks enjoy dueling and sport of all kind.
Wyrd Gnomes. Gnomes with gifts for the arcane, touched by their long time spent in the Shadesmere.
Humans
Umbral Humans. Many humans have come to Shadesmere as servants or dupes of the shadow fey, and some have fallen into the realm by misadventure, straying from a shadow road. Most, however, descend from those who sought the place out to acquire power, study magic, or escape troubles of their own. Both Changelings and Gifted are variants of Umbral humans.
Changelings. Humans that have been spirited away to the Shadesmere. Many were brought as servitors to the first Shadow fey.
The Gifted. Humans touched by their pacts with fey creatures, The Gifted would better be called The Cursed. Tempted by dark pacts and promises, they are broken souls.
Undead
Oftentimes undead find that the Shadesmere is more welcoming to their kind. At the very least, they can escape the baneful light of the sun in such a place. Myriad undead haunt the Shadesmere, just as many sentient as those that aren't. They often form their own well-protected socieities, though some settlements are more welcoming to them than others.
Darakhul. Often viewed as flesh-eating scavengers, darakhul can make for a fearsome sight for those unused to their kind. A darakhul can rise from any mortal race corpses and thus will retain some features from their mortal life.
Stygian Shades. Wandering ghosts, often lost and barely clinging on to a semblance of who they were before they were consigned to darkness.
Outsiders
Shadesmere is a strange, transient place. The vast majority of creatures who inhabit it cannot truly claim to be natives, having at one time or another descended from creatures that either found their way on the winding shadow roads or became hopelessly lost.
Unbound Satarre. Strange reptillian travelers drawn by the mysteries of the Shadesmere.
Note: A member of any race could easily find themselves caught in the ebbing tides. Any fey (trolls, pixies, sprites, dryads), number of undead (skeletons, vampires), and beastfolk/werebeasts would also be likely canidates for this setting.
Any creautres who are not native to Shadesmere may suffer effects of Shadow Corruption.