Extend the recently changed behavior for cursed potion of invisibility. Monsters won't drink potions of invisibility if already invisible so can't accidentally or voluntarily make themselves visible again, but let player make them become visible by hitting them with thrown or wielded cursed potion of invisibility. They don't have any concept of temporary invisibility that might let them remain invisible while losing permanent invisibility, so they just lose the latter and immediately become visible.
170 KiB
170 KiB