At the menu select screen, press one of the following for the desired affect. Only one code can be used at a time.

Effect	Code
All weapons	A, B, C, A, C, A, A, A, A, A.
All weapons and invincible	A, B, C, A, C, C, B, B, A, C.
Start with 2 extra bombs	A, C, B, B, A, A, C, C, B, C.
Start with 4 extra credits	A, A, B, B, C, C, A, B, C, B.