The Shadowfell
The Shadowfell is one of the "Mirror Planes" of the 4th edition cosmology, and is where the Shadowfell Domains lie. Whilst sometimes compared to the Plane of Shadow, as many creatures associated with that plane were relocated here in the new cosmology, the comparison is inaccurate. The Shadowfell is best defined as "The Plane of Death"; it is the realm to which mortal souls travel upon their demise before passing on to their final fate, as well as the wellspring from which the undead and the magical energies of necromancy are born. Whilst it is a "Mirror Plane", in that it mimics the general topography and geography of the Prime Material Plane, it lacks the association with elemental darkness found in the Plane of Shadow. There is a certain dimness to the natural light and patches of unearthly darkness, but most of the Shadowfell's distortions warp the landscape in a way to induce and amplify feelings of futility, dread, despair, fear and sorrow.
Travel to the Shadowfell is not for the weak or the faint of heart. In addition to an abundance of undead and powerful monsters, the Shadowfell has a potent planar malaise which works upon the minds of mortal visitors, slowly corrupting them in various ways, which can include the amplification of vices, a deep, cloying sense of apathy, intense despair and melancholy, and outbreaks of madness. Long-term residents or nativeborn denizens of the Shadowfell often come off as evil and/or insane to varying degrees in the perspective of outsiders.
Native races of the Shadowfell include the shadar-kai, dusk elves, vryloka and revenants.
Shadowfell Domains are a peculiar planar phenomena of the Shadowfell that roughly equates to the means by which new domains are formed in the original Demiplane of Dread. When an individual commits an act of great evil, that evil may "stain" the Shadowfell reflection of the region, causing it to be warped into a twisted realm based on that individual's crime(s). The individual who created the Shadowfell Domain becomes metaphysically bound to it as its Darklord; some find themselves being reborn in the Shadowfell Domain upon their death, others are pulled across the planes into it whilst they live. The Darklord cannot leave their Shadowfell Domain, despite typically gaining great mystical powers as a result of their bond; only a final death by breaking their curse can sever this planar bond.
