Death and the Fey

Strictly speaking, the Fey are immortal, in that they will not die of natural causes such as age, or disease, (or at least, none has ever been known to do so,) and they cannot be permanently slain in the traditional sense by material means, but there are magical methods of permanently destroying them.
When a Fey being is "killed", its flesh dies and, in time, decays, but as Fey are more spirit than flesh, that spirit entity lives on, generally retaining it's memories, and its knowledge of 'self'. If its flesh is protected, then in time, the spirit will reincorporate itself, reclaiming its fleshy form not as an undead thing, but as a living breathing entity. This process may take days, or weeks, and occasionally, even longer.
Unprotected husks might become corrupted by void or shadow, or devoured by animals or insects. Likewise, a Fey's enemies might destroy it's husk with fire, denying it a body to return to. In such instances, the spirit must regenerate its flesh, which might take years. During this time, the spirit is at risk of becoming 'lost', either losing its motivation to continue the monumental task of regenerating its flesh, or simply forgetting to do so. Wandering spirits are common enough in the Fey realms, and it is difficult even for Fey arcanists to identify them, and help them to return from such a state. Some such confused spirits are hostile, and they can be dangerous to mortals.
If a lost spirit comes upon a husk that is not its own, it might lay claim to it, creating a sort of animated dead. The Fey guard the husks of loved ones strongly against such intrusion, since the only ways to remove the spirit are to call it by its true name, or destroy the husk.
Fey spirits can also become corrupted while still within their own flesh, and in such cases, the bond between body and soul can become damaged, and the flesh begin to decay. Thus corrupted Fey are also seen as something akin to the undead.

Type

Metaphysical, Arcane