Enter "KILLZONE" as a password to play the mystery arena. This level is full of bombs, bonus letters and gold bars and towards the end of this arena just by the exit is a large orange and blue gem stone. Picking it up will make the screen flash and activate the main cheat mode.
Entering "CHEATOFF" as a password will deactivate the cheat mode.
Also enter "SHOW X ?" as a password to reveal all of the hidden teleporters in the game by placing a white X over them. Enter this a second time to turn the option off.
And finaly, enter "TOOFAST?" as a password to speed up the game. Entering "NORMAL" returns the speed setting to normal.