One of the first Neo Geo pocket Emulators, titled R.A.P.E? [Rather a Pokemon Emulator?] was able to somehow open up a special debug menu by pressing start [or 'o'] at the starting screen. Here you are able to choose from several different options.

'Beginning' allows you to start from whichever level you want to. Test stage 1 and 2 are simply Neo South Island Zone act 1 and 2, which will crash the emulator. 'Go to room' will take you to the puzzle and option room, 'direction' will take you to the ending scenes, and 'sound test' is simply that.

The Debug screen allows you to turn on a lot of little things, like a debug display telling you your coordinates. Atk and Bdy display will will cause little 90 degree angles to appear around Sonic and enemies.

Here are some examples of the displays, including the Debug, Atk and Bdy displays around the characters.

When in debug mode, pressing action button 2 [or 'B' in R.A.P.E?] Will cause your character to turn into Tails! Tails is used in the link up game where you must get enough rings or get to the end. If you change in the middle of a jump they will keep their previous palette for a second until they reach the ground.

You can only do this by going through the debug options screen.

By an odd coincidence, the game will also cause Sonic to float if you have pressed out of the emulator screen and back, or by pressing A and B buttons together. You cannot change into other bits and pieces here, just move around.