Unlock Bad Buddy Code:
To enable free switching between 2 players go to the 'Game select' screen and highlight 'Erase Data' and press B, A, Down, B, Up, Down, Down, Y, A.

Start with 50 Lives:
At the 'File Select' Screen select 'Erase Game' which will flash and then press B, A, R, R, A, L and choose a game.

Practice the Bonus Rounds:
Press Down, Y, Down, Down, Y when the Intro is playing.

Unlock Music Test:
Highlight 'Erase game' and press Down, A, R, B, Y, Down, A, Y and then press Select.