Level select:
Pause the game and press Up, Left, Down, R2, Right, Square, X.

Full health:
Pause the game and press R1, Triangle, L1, Left, Triangle, Circle, X.

Red beam mode:
Pause the game and press Right, Up, Left, Circle, Up, Circle, Circle.

Ten additional missiles:
Pause the game and press X, Circle, R1, Right, Triangle, X, Triangle.

Ten additional grenades
Pause the game and press R1, X, R1, Right, Square, Right, Square.

Unlimited lives:
Begin a game and reach the Craterscape level. Then, take the extra life located behind the pillar on the bridge at the start of the level. After the total number of lives have increased, press Start, Select, and choose the "Quit" option. Select "Yes" to confirm to return to the title screen. Select the "Start" and "Continue current game" options to restart at the Craterscape level. Collect the extra life again from the pillar and repeat this process to accumulate an unlimited amount of lives.