Bottles' Revenge

Bottles' Revenge is a secret game mode which was not made playable in the final version of Banjo-Tooie for unknown reasons. 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 by pressing (R) and use it to attack player 1.

Curiously, although Bottles' Revenge is not unlockable by normal means, it still remains within the game and can be played using a Game Shark or other hacking device.

Video
http://www.youtube.com/watch?v=YDTiC0frGE0