A Cheat menu with options for full weapons, infinite ammunition, no clipping and God mode will appear if you pause the game and hold L then press Left, Up, A, Up, Left, A, Start, Select.
Throw more than one pipe bomb:
To be able to throw more than one Pipe bomb select the Pipe bomb and throw it and then press and release Select to be able to throw another.
Shrink Ray Gun warning:
Don’t walk next to an enemy and shrink them as you will also shrink.
Freeze Gun warning:
Don’t fire the Freeze gun if you walk next to a wall as you will freeze instead of the wall.
Use the Freeze gun when you see an Octobrain and when it is frozen it will fall and smash. Save bullets and rockets by doing this.