When the animated screen appears after the title screen, type "LETS LOOK AT WHAT YOU COULD HAVE WON". Next type "SUPER SMASHING GREAT" and press P to unpause the game and press the joystick button to start the game. This will give you infinite energy and will enable the following keys:

F1-F5 Warp to corresponding level (1-5)
1-8 Gain object 1-8
TAB Open all exits