Codes note:

Some codes destroy or modify the game data, so it may not be possible 
to win the game. Some codes store their status in nvRAM. 

Speed mode:

Press C to display the game menu, then press P, Up, LS(2), C, RS, Up, 
Down. A voice will say "no problem" to confirm correct code entry. 
Rachel and Gideon will move quicker during the interactive portion 
of the game. 

Night vision:

Press C to display the game menu, then press P, Up, B, C, Up, B. A 
voice will say "night vision" to confirm correct code entry. The 
game's graphics will be shaded in red and green. Enter the code 
again to return to normal mode. 

Silly mode:

Start a new game and press Down(3), Up(2), LS(2), RS(2) at the 
character selection screen. Then, press A over the character to be 
played. Gideon will appear as a clown, Rachel will grow a beard, 
and both characters will make a silly comment before the game starts. 
The characters will then appear normal after the game begins. 

Debug mode:

Press C to display the game menu, then press P, LS, A, Down, C, RS, 
A, P, Down, Up, Down. A voice will say "I know everything there is 
to know about Hell" to confirm correct code entry. Press C and 
select the "Game" option. Four new items will appear. 

"Go To Map" will allow access to any game scene.
"Get Object" will allow access to all objects in the game.
"Cinematics" will display all the FMV segments of the game.
"Advance Time" will add one day to the game time. 

Quick speech:

Press C to display the game menu, then press P, Up, C, LS, U, X. 
A voice will say "hey, sounds good to me, man" to confirm correct 
code entry. Only the first few words of each speaking segment will 
be played, speeding up the game.