u/PsychologicalUnit446

Mutantification is the irreversible process that students, pros, or anyone with Quirks undergo when their psychological state becomes too unstable. Since there is no cure for mutantification, it is treated by the non-Mutantified humans the same way as death; they are laid to rest in The Cellar, and funerals are held. Mutantified people appear to become calm in darkness.
When someone mutantifies, their appearance changes to a monochrome tint coming from the dulling of their colours from their skin, hair, and more, and they have purple glowing sclera, becomes twice their size, Quirks then become unusable. But when in darkness, their eyes become dilated, and in a sitting position
And Mutantified Quirk users are seemingly mindless, feral, hyper-aggressive beasts that chase down and ruthlessly attack anyone and anything in their way. It is currently unknown if there remains any memories or consciousness of the victim after transformation. Negative emotions or memories might still remain. Although those Mutantified become vicious and cannot be returned to lucidity, the darkness seems to bring some stability to them and can even cause them to be aware and less mindless, but they have no ability to speak, only uttering hisses like a snake/cat, growls, and scratchy static noises.
How it is processed is by when a character's psychological state becomes too unstable, whether that be through depression, anxiety, psychosis, or other negative mental states, as it may indicate one of the main factors of the mutating process specifically is low self-esteem and hopelessness. Soon-to-Mutantified characters are also described as being 'unpleasent to be around', due to irritability and ramblings. Panic attacks may also be a sign of near mutantification. And signs of mutantifcation if that person’s colours become dull, or suddenly becoming tall when depressed