Hidden mode 
At the mode selection screen, press 
Right, Down, Right, X, Up, X, X, Y, Down, Right, Down, Right, X, Y. 
If you entered the code correctly, you will hear the sound of a gun. 

Mirrored levels 
At the mode selection screen, press 
Left, Left, Right, X, Down, Down, Up, Y, Up, Right, Down, Up, Left, Down, X. 
If you entered the code correctly, you will hear the sound of a gun.

First person view 
At the mode selection screen, press 
Up, Up, up, Up, Down, Down, Down, Down. 
If you entered the code correctly, you will hear the sound of a gun.

Turbo mode 
At the mode selection screen, press 
Down, Y, Up, X, Y, Down, Right, Down, Right, X, Y. 
If you entered the code correctly, you will hear the sound of a gun.

Love mode 
At the mode selection screen, press 
Left, Right, Right, X, Y. 
If you entered the code correctly, you will hear the sound of a gun.

Night mode 
At the mode selection screen, press 
Up, Right, Down, Left, Up, X, Y. 
If you entered the code correctly, you will hear the sound of a gun.

No crosshair 
At the mode selection screen, press 
Right, Right, Right, X. 
If you entered the code correctly, you will hear the sound of a gun.

No scope 
At the mode selection screen, press 
Right, Down, Right, X, Right, Down, Right, X. 
If you entered the code correctly, you will hear the sound of a gun.

No enemy cursor 
At the mode selection screen, press 
Right, Right, Right, Right, Left, Down, Up, Right. 
If you entered the code correctly, you will hear the sound of a gun.

Exchange a half of life for 5 seconds 
Pause the game in arcade mode and press 
Up, Up, Down, Down, Left, Right, Left, Right, A, B. 
If you entered the code correctly, you will hear the sound of a gun.

Exchange 5 seconds for half of life 
Pause the game in arcade mode and press 
B, A, Right, Left, Right, Left, Down, Down, Up, Up. 
If you entered the code correctly, you will hear the sound of a gun.