Yogi's Big Clean Up

On the screen right after the title screen, the one with the
animation, type "LETS LOOK AT WHAT YOU COULD HAVE WON".  Then type
"SUPER SMASHING GREAT".  Now 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  Skip to corresponding level.
1-8    Select object.
TAB    Open exits.

On the same screen type "FRITH MODE". Not sure what this does.