Bug!

Go to Help, then About Bug.  

Hold down the SHIFT key and click Bug's right 
pupil. A screen should appear. Type "babyseals" 
and press Yikes! or Wow! (NOT OK!). 

Press to the right of Help and a cheat 
menu should appear.

Flying bug = Activate the cheat menu, select cheat, 
             then hold y in gameplay.

Level skip = Activate the cheat menu, select cheat, 
             press duck up or to skip down duck+down.

Kill Sonic = In reptilia use the the flying bug cheat and 
             fly around until you see rocks shaped like 
             "GO"and a track with Sonic on it.