A soul split and badly reunited into an object-bound half-life — undead, near-powerless, hard to kill, often used as quest-giver NPCs.
A Withering Spirit is what Mordecai identifies in the possessed Lika doll head housing Psamathe. When a soul splits, the halves try to reunite like magnets, but only in a proper vessel; if reunification fails — or the vessel is wrong — the result is a withering spirit: not alive, not dead, hard now to kill, and largely powerless, haunting an object. The dungeon frequently uses them as quest-giving NPCs; one season made an entire floor of withering-spirit-possessed weapons.
They differ from the more dangerous purpose-built kind like the third-floor 'soul leech capacitor' Remex; these are a stabler version. Freeing one requires an exorcism — complicated further when the spirit is a minor deity like Psamathe.
Has no form of its own; manifests through and haunts whatever object it's bound to (here, a latex doll head).
A class of object-bound, half-alive spirit — near-powerless, hard to kill, and often a quest-giver.