Enter all cheats in the main menu!

9 Credits:
X, A, L, R and left- now hold the L-buttonand enter X, C, Z, A, right,
right!

Sustained fire:
Hold the B-button and enter Y, right, left, X, Z, L and R!

Two new skill level:
Hold the X-button and enter Z, C, L, B, left, R and L!