Extra rounds Enter L, R, L, R, L, R, Right, Select at the title screen. A door should appear on level 20. Touch it and you should be able to play these extra rounds.
Shoe power-up mode You can get your shoe power up by entering this code: Select, R, L, Left, Right, R, Select, Right at the title screen.
Super Bubble Bobble Beat the Classic version Boss using two players. Then enter the following code at the title screen: Left, R, Left, Select, Left, L, Left, Select.
2006 Version Cheats
Unlock Levels 91 to 100 Before you get to level 91 you need to accumulate ninte letters. To get a letter you need to kill at least four enemies with a single Super Bubble, they will drop a key which you need to pick up. This will unlock the boss for each set of 10 levels. After each boss is defeated it will drop a letter instead of the big gem. If you get all nine you will have unlocked the final ten levels.
Play as Robolun Complete all 100 2006 version levels and you will unlock Robolun as a playable character.
Play as Lovelun Complete all 100 2006 version levels with Robolun and you will unlock Lovelun as a playable character.