Unlock 9 Continues:
Hold Down, Left + A + C and then release and press 'Start'.

Unlock Level Select:
Select Arcade mode and hold Down, Left + B and 'Start' at the 'Character Selection' screen. Then using your D-pad change the number that appears at the upper left corner of the screen to the level you want to play.

At the Arcade mode 'Character Select' screen hold 'Down + Left' and then press and hold 'A + C' and release ALL four buttons and select a character.

At the Arcade mode 'Character Select' screen hold 'Down + Left' and press 'B + Start'.