Press and hold W+A+X keys while playing. You will get all 9 Weapons, Full Life, & Proximity Mines. However, your score will go to 0 every time you use the cheat.
Start the game by typing C7 LEVEL1DIAGNOSTIC. Now you can use these Cheats...
Backspace+G = God Mode. Backspace+W = Level warp. Backspace+N = No clipping. Backspace+R = Puts a skull in front of character. Backspace+I = Increases score.