At the title screen press Down, Up, Down, Up, Right, Down, Left, Down, Up, Down.
To use it, press any of the following keys while playing:
L1 - Warp to previous level
R1 - Warp to next level
R2 - View debug menu
R1 - Hide debug menu
To play the original version of Bubble Bobble press Right, Left, Up, Down, Up, Down,
Up at the title screen. In this mode you can enter the diamond rooms even if you die.
Thunder Bubble Glitch
Do the Debug Code. During the game, press R2 to bring up the debug menu. Go to map 63
and press L2. You will go to stage 100 where there are thunder bubbles. Press R2 again and
go to map 0 and press L2. You will have the thunder bubbles with you on stage 1. Now you
can easily beat the game.