On the title screen, type "ZEGOOLI" to start at level 8 or type "MRCLINK" start at level 15.
During play, type "BIGGIGBIB". The following keys will now be active:
'F1' ---- Skip back a level
'F2' ---- Skip forward a level
'SPACE' - Fly mode
Holding down 'FIRE' while in fly mode will make you travel twice as fast.