Black Key

Mario obtaining the Black Key.

Black Keys are items in Paper Mario: The Thousand-Year Door that open the four Black treasure chests. Each chest contains a Black Chest Demon that "curses" Mario and gives him a new Paper ability on the field. The keys are usually easy to find and shouldn't be too far from the chest.

There is no known reason why the keys exist, since the Shadow Queen's curse was supposed to leave them trapped for eternity.

Keys
Black Key \| Blue Key \| Card Key \| Castle Bleck Key \| Elevator Key \| Fortress Key \| House Key \| Key \| Luigi Key \| Mario Key \| Odd Key \| Palace Key \| Pedestal Key \| Random House Key \| Red Key \| Ruins Key \| Shop Key \| Skeleton Key \| Station Key \| Steeple Key \| Storage Key \| Storeroom Key \| Warehouse Key \| Wario Key \| Yakkey