Enter the following codes quickly at the 'Press Start' screen: 
Goodies option:
Press Triangle, Square, Circle, Left, Square, Triangle, Square, Circle, Left, Square. Go to the 'optioons' menu to find a new selection. 

Nakomi mode:
Press Up, Up, Down, Down, Left, Right, Left, Right, X, Circle. 

Big head Player:
Press Square, Circle, Circle, Square, Up, Square, Circle, Circle, Square, Triangle. 

Big head Aliens:
Press Square, Circle, Circle, Square, Up, Square, Circle, Circle, Square, X. 

Speed run:
Press X, Square, Triangle, Circle, X, Square, Triangle, Circle, L2, R2. 

Grayscale graphics:
Press X(2), Triangle(2), Square(2), Circle(2), Up, Down 

Sepia Graphics:
Press Left 10 times.




GameShark Codes
Have All Weapons P1	300936810003
			300936820003
			300936830003
			300936840003

 
Infinite Ammo P1	800936b60006

 
Infinite Lives P1	800936bc0005