Serious Sam cheats and cheat codes for XBox

Cheat mode
Click and hold the Left thumb-stick and push Black, White, Y buttons 
on your controller while you are at the main menu. This will unlock 
the "Cheats" option in the main menu. After activated the cheat mode, 
push Start button while playing to bring up the cheat menu. 

Developer cheat mode:
Click and hold the Left thumb-stick and push Black, White, Y, Y, Y 
on your controller while you are at the main menu. This will unlock 
the "Cheats" option and "Developer Cheats" options in the main menu. 
The developer cheat mode will allow you to jump to certain checkpoints.

Mental mode
Finish the game in Serious mode, then begin a new game. 

Unlock secret stage:
If you play on the Valley Of The Kings level, destroy all the statues 
to get access to the hidden stage.

Unlock all characters:
Play in single player mode with Serious Sam. When the 1st stage load, 
save the game then exit. Enter to one player mode and begin a new game by 
pressing Y button. You will see a messed up name.
Do not delete that name, just choose "Done". 
Allow the game to load and save, then exit and go to one player mode. 
If done correctly, you will see Serious Sammy there. Repeat these steps 
until you get all the charcaters.