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.
GENESIS
Sonic Spinball
Stage Select - At title press A, Down, B, Down, C, Down, A, B, Up, A, C, Up, B, C, Up(ring)
Hold A - Lava Powerhouse
Hold B - Machine
Hold C - Showdown
 
Multi-ball Stage - Collect all rings then find and enter the gate