At the  game-select  screen, pick Bubble Bobble.  Then, at the  Bubble
Bobble title screen, press Down,  Up,  Down,  Up,  Right,  Down, Left,
Down, Up, Down. You'll hear a chime.  Start a game and press R2 at any
time.  This brings up a debug menu that lets you warp to any level and
increases you lives. Press L2 to exit the debug menu.