Classic version: Bonus rounds
Press [L], [R], [L], [R], [L], [R], [Right], [Select] at the title screen in the Classic version. Touch the door that now appears in level 20 to start the bonus rounds.
Classic version: Shoe power-up mode
Press [Select], [R], [L], [Left], [Right], [R], [Select], [Right] at the title screen in the Classic version.
Classic version: Super Bubble Bobble
Defeat the Classic version Boss using two players. Then, press [Left], [R], [Left], [Select], [Left], [L], [Left], [Select] in the Classic version.
New version: Levels 91 to 100
The final ten levels in New version are only accessible after you collect nine letters throughout the game. You must kill at least four enemies with a single Super Bubble, then collect the key that they drop. After defeating the Boss of that group of levels, it will drop a letter instead of the big gem. You must collect a letter from every Boss in the game (nine total) to unlock the final ten levels.
New version: Play as Robolun
Successfully complete all 100 New version levels.
New version: Play as Lovelun
Successfully complete all 100 New version levels as Robolun.