Welcome to the FX codes
 
Blue codes are old, they can be found everywhere or in a few places.
 
Red codes I've found in mags and sites but I can't get them to work. (they are probably fake)
 
Green codes- I don't have this game so I can't test it.
 
Orange codes are discovered by me, you might find them elsewhere but they were here first.
GAME GEAR
Sonic Chaos
Sound Test - Down, Down, Up, Up, Left, Right, Left, Right, Start(boink)
 
Fireball - In Sound Test Press Down, Forward, 1
 
Level Select - Up, Up, Down, Down, Right, Left, Right, Left, Start(boink)
 
The Magic Number - Hit the sign at the end with 77 rings for a 1up