Bomberman 64: The Second Attack Cheats

CPU characters in battle mode:
Hold Z and press A at the battle mode character selection screen to use the CPU characters. 

Music option:
Finish story mode to unlock the music option.

Battle Royal mode:
By winning the gold cup in Survival mode.

King and Knights mode:
By winning the gold cup in Battle Royal mode.

Key Trial mode:
By winning the gold cup in King and Knights mode.

Score Attack mode:
By winning the gold cup in Key Trial mode.

Alternate title screen:
Finish the game to change the title screen to display one of Pommy's different levels with a blue background with clouds.

Getting the Dark Bomb:
First, throw a lava toward him. He will shoot with the bird thing. Keep doing this until you defeat him.