Fellsoul

A soul which has undergone mental collapse, causing it to become trapped inside a monstrous ichor-formed version of itself which lashes out in accordance with the nature of the collapse.

Fellsouls are often notably more powerful than their originators, as the loss of stability allows for it to be disregarded when resonating in favor of the self-damaging spiral, which achieves extreme speeds although with a disharmonic moment, slowly eroding the soul from within.