At the Title screen, press X, B, Y, A, X, B, Y, A, X, B, Y, A, X, B, Y.
Easy Mode
At the title screen, press: X, B, Y, A, A, A, A. If entered correctly, you will hear a voice saying: "Easy Game". When playing the game now, your weapons will charge fast !
Unlock Hyper Laser
Complete the game on Normal difficulty to unlock the Hyper Laser.
Unlock Spread Rocket
Complete the game on Easy difficulty to unlock the Spread Rocket.