Debug Mode
At the title screen press Down, Up, Down, Up, Right, Down, Left, Down, Up, Down.
To use press any of the following keys while playing
L1 - Warp to previous level
L2 - View Debug menu
R1 - Warp to next level
R2 - Hide Debug menu
Original Game:
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.