Bottles' Revenge is a secret game mode which was not made playable in the final version of Banjo-Tooie because it was not completly debugged. It is uncertain exactly what would trigger the event, but Bottles' ghost would become evil and adopt a devilish appearance, usually known as Devil Bottles. This Devil Bottles would follow the player around and take possession of the nearest enemy, allowing a second player with another controller to take control of it and use it to attack Player 1.
If player 1 enters a boss fight, Devil Bottles will disappear until the fight is over. Rare has stated they originally intended to have Devil Bottles control bosses as well, but since they believed that the disruption of a boss' attack pattern raised the difficulty too much, they left it out.
Curiously, although Bottles' Revenge is not unlockable by normal means, it still remains within the game and can be played using a hacking device such as a GameShark or by downloading the Banjo-Tooie ROM and playing it on an emulator.