TheGameSite: Tips, Cheats, Walkthroughs: N64: Bomberman 64
EXTRA BATTLE MODE COURSES
This code adds four extra battle mode courses: In the Gutter, Sea Sick, Blizzard Battle, and Lost at Sea.
Instructions: On the Title screen, highlight "Battle" so that it is flashing. Rapidly tap the Start button until you hear a tone. When you select your characters and choose your stage, the four extra stages will be available. Note: Getting this code to work can be very difficult, as you must press the Start button very rapidly.