Various cheats
     Enter these codes on the Credits screen at the main menu.

Cheat code:                                      Effect:
B, Y, L                                          All Upgrades
B, Black, R                                      Invincibility
B, Black, Y                                      Level Select
Select the credits option at the main menu, 
then press B, Y, L while watching it. 
                                                 All Upgrades
Select the credits option at the main menu, 
then press B, BLACK, R while watching it.        Invincibility