Black chest

The Black chest is an object that appears in Paper Mario: The Thousand-Year Door.

History
The Black chest contain the souls of the Four Heroes who helped defeat the Shadow Queen 1,000 years ago. However, they have become Black Chest Demons who do nothing but "curse" Mario whenever he opens one (though this always give him a helpful ability). A Black Key is always needed to open a Black chest but they are usually found nearby. These are the locations of the four Black chests in the game: After a Black chest is opened and the Black Chest Demon goes away, the Black chest will stay there opened for the rest of the game.
 * Rogueport Sewers on a lower floor in a room.
 * Hooktail Castle past the jailing room before the spiked ceiling room.
 * Twilight Town in the storeroom of the item shop.
 * Pirate's Grotto inside an old ship.