Brain Dead

Brain Dead trades the cat's mind for raw growth potential. The cat suffers a brutal -10 Intelligence and -5 Charisma, but in exchange every future level-up grants twice the usual stat rolls and one additional reroll to find the spread you want. It is the "Learn unfathomably powerful abilities" outcome of the Monkey Paw event, where the paw floods the cat's brain with knowledge until most of it is paved over, and as part of that wish the cat is also immediately leveled up twice on the spot for a free head start.

The best homes for Brain Dead are cats that do not lean on Intelligence or Charisma to function: melee bruisers, physical-damage classes, and summoners whose minions do the talking. On those cats, the disorder is almost pure upside, because you were never going to cast INT-scaled spells or barter with merchants for serious discounts anyway. Stacked over a long run, the doubled level-up gains compound into a cat that massively out-scales untreated siblings by the endgame. Pair it with disorders that also avoid interfering with combat, like The Shining or Immortal, to build a cat that levels faster and fights smarter at the same time.

Because Brain Dead is heritable, it is worth locking into a breeding line the moment you find it. It can also be acquired from events, the Monkey Paw, or an Organ Grinder Disorder Syringe, but breeding is by far the most reliable way to put it on a cat whose stat spread welcomes the INT/CHA hit. If you are weighing Brain Dead against most other disorders, take Brain Dead. If you are weighing it against another purely beneficial disorder, stack both: the Monkey Paw may have meant this one as a curse, but on the right cat it is the single most valuable disorder the game hands out.