Goodies option:
Press Triangle, Square, Circle, Left, Square, Triangle, 
Square, Circle, Left, Square within three seconds at 
the "Press Start" screen. An additional selection
will appear at the end of the options menu that 
allows level selection, all weapons, unlimited ammunition, 
and the ability to view the FMV sequences. 

Stage select
Enable the "Goodies option" code. Then, press Left, 
Right, X, Triangle, Left, Up within three seconds at 
the "Press Start" screen. A white screen flash, sound
effect, and display of the cheat name will confirm 
correct code entry. An option that will allow selection 
of an individual stage within a level will become 
available.

Note: Enabling this code may cause music and graphic problems. 

Nakomi mode
Press Up(2), Down(2), Left, Right, Left, Right, X, Circle 
within three seconds at the "Press Start" screen. A white 
screen flash, sound effect, and display of the cheat name 
will confirm correct code entry. All 3D characters except the 
Boss will be flattened. 

Big head player
Press Square, Circle(2), Square, Up, Square, Circle(2), Square, 
Triangle within three seconds at the "Press Start" screen. 
A white screen flash, sound effect, and display of the cheat 
name will confirm correct code entry. 

Big Head aliens
Press Square, Circle(2), Square, Up, Square, Circle(2), Square, 
X within three seconds at the "Press Start" screen. A white 
screen flash, sound effect, and display of the cheat name 
will confirm correct code entry. Note: This code does not 
affect the Boss. 

Turbo mode
Press X, Square, Triangle, Circle, X, Square, Triangle, Circle, 
L2, R2 within three seconds at the "Press Start" screen. A white 
screen flash, sound effect, and display of the cheat name will 
confirm correct code entry. Press Circle during game play to run 
faster. 

Note: This will also use any item currently being held by your 
character. 

Grayscale graphics
Press X(2), Triangle(2), Square(2), Circle(2), Up, Down within 
three seconds at the "Press Start" screen. A white screen flash, 
sound effect, and display of the cheat name will confirm correct 
code entry. 

Sepia graphics
Press Left(10) within three seconds at the "Press Start" screen. 
A white screen flash, sound effect, and display of the cheat name 
will confirm correct code entry.