Rampage World Tour is the first Rampage title for Gameboy Color but it sadly omitted an official 2-player link cable co-op mode. However, the developers started this feature and left this option hidden in the final built.
By entering a secret code on the main menu (hold SELECT, then hit UP, DOWN, LEFT, RIGHT, DOWN, UP), the unfinished multiplayer mode becomes available. It is rather buggy and often freezes as the games moves to the next stage. Still, this paved the way for the co-op mode in the GBC sequel Rampage 2: Universal Tour.
