I'm running a campaign where the players have found themselves in the Shadowfell. I have no idea what sorts of monsters or people would be iconic for this realm. Is there a comprehensive list somewhere? We happen to be playing 5e, but I can make use of information from any edition.
Detailed information on the 5e version of the Shadowfell is still pending (hopefully in the Dungeon Master's Guide!) but here are some typical inhabitants from 4e:
- Shadar-Kai, near-humans with tattoos and scars that rejoice in battle and have shadowy abilities.
- Shadow creatures (none are in the Basic Rules bestiary, and the type may not exist at all in 5e).
- Ghosts of the dead on their way to their final destination.
- Corporeal undead, typically the result of ghosts who refused to pass on.
- Any horror-themed creature, as the Shadowfell is basically Spooky Halloween World.
Given the limited creatures available in the Basic Rules, I'd provide a lot of undead and reskin some other creatures: turn wolves into "balehounds" and ogres into "flesh terrors" and so on.
You can generally assume that each normal race has a Shadowfell subrace or equivalent with gray skin, shadow-themed abilities, and more piercings.
In 4th edition, the major races of the Shadowfell, as established by Manual of the Planes, Heroes of Shadow, and The Shadowfell: Gloomwrought and Beyond, are thus:
- Spirits of the Dead: The souls of the departed pass through the Shadowfell before they are sent on to their ultimate fate, such as being sent to the astral dominions (Outer Planes, in 5e).
- Undead: Undead in both sapient and nonsapient forms throng the Shadowfell.
- Death Giants: Corrupted giants who must feed on the souls of other creatures to sustain their corporeal existence.
- Nightwalkers: Extremely powerful fiend-like undead monsters.
- Sorrowsworn: Psychopomps, essentially; powerful angel or fiend-like spirit-beings who exist to safeguard the sanctity of death and to protect the Shadowfell from abuse.
- Shadar-kai: Humans who sought immortality through a pact with the Raven Queen; they seek constant stimulation and excitement, which keeps them young and vibrant, else they will fade away into nothing.
- Dark Ones: Halfling-like small humanoids who shun bright light and often inhabit the Underdark as well as the Shadowfell. They have a tendency towards xenophobia that they often use as an excuse to steal from other races to support their own colonies, but they can peacefully integrate amongst other races.
- Incunabula: A race of necromancer-diviners obsessed with harvesting secrets who inhabit cities in the Shadowfell's Underdark. Descend from a knowledge-obsessed necromancer who stole the swaddling clothes of a stillborn god to harvest their power.
- Dhampirs: The hybrid offspring of living humanoids and vampires.
- Revenants: Extremely rare, the souls of the dead granted a new lease on life at the behest of mysterious powers in a strange body - humanoid, but with subtle crow-like features. Basically, think "The Crow".
- Shade: Humans who have performed a ritual that sacrifices a fragment of their soul to imbue them with innate shadow-manipulating abilities.
- Shadowborn: Any humanoid type creature from the mortal world might be found living in the Shadowfell. Those that survive give rise to descendants called "Shadowborn", typically marked by paler coloration, grimmer features, and tendencies towards amorality, melancholia, or insanity as a result of the Shadowfell's planar influence. The most common Shadowborn "subraces" are humans, elves (Dusk Elves), eladrin (the Pale Court), halflings and dwarves.
- Vistani: A multiracial culture of wagon-dwelling magic-practicing nomads who travel across the planes, but who have a strange fondness for the Shadowfell.
- Vryloka: A human subrace descended from aristocratic families who made an unholy pledge for power, imbuing them with a semblance of the powers of vampires.
In general, 5e hasn't really touched the Shadowfell too much, as they want to avoid dwelling too much on anything directly tied to 4e. As far as I'm aware, in 5th edition, the races most explicitly tied to the Shadowfell thus far are Shadar-kai, Sorrowsworn, Dark Ones, Nagpa and Undead.