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 2
Play as Miles - At Title Screen press Up, Down, Down, Down, Up(ring) Anything that once said "Tails" Will say Miles.
 
14 Continues - In Options play songs 1,1,2,4(oil ocean music won't stop)
 
Extra Options During Game - In Options play songs
19,65,9,17(ring)
When paused    A=Reset    Hold B=Slo-Mo    C=Frame Skip
 
Level Select and New Sound Test - After Extra Options During Game code press Start on Sound Test, now hold A, Start at Title Screen
 
All Chaos Emeralds - At the Level Select Sound Test play songs 4,1,2,6(all emeralds sound effect)
 
Debug - At the Level Select Sound Test play songs 1,9,9,2,1,1,2,4(ring)hold A when selecting a level
B=Enter/Exit Debug    A=Change Item    C=Place Item
 
Speedy Characters - In Oil Ocean 2 there are two machines that a rocket platform feeds you in and bounces you out the top, go to the second one and hold Right when being fed through the object is to land on the spikes and bounce back to the canon (You can use debug and create a canon that points down near some spikes)
 
Use These With Debug
 
Green and Black Sonic - In Emerald Hill enter debug and turn into the item that looks invisible, keep hitting Right, C and place at least 60 waterfalls, hold Left for a 5 seconds, exit debug then hold right to run through the waterfalls. (if it doesn't work add more waterfalls)
 
Two Tails in Sky Chase - Create and hit a Transfer Box, when you hear Sonic die press B, wait for the SCOR numbers to stop moving then press B again
 
Supersonic and Super Tails - Turn into Supersonic, Create and hit a Transfer Box, Now you have Super Tails and fake Supersonic, get hit by something to stop being fake Supersonic, now get 50 Rings and jump (Place rings on Tails to speed up the process)
 
Play as Gold Sonic - In options switch to "Sonic Alone" then do the level select code, then the debug and all chaos emeralds codes, become Supersonic then create and hit a transfer box (Gold Sonic is not invincible, can get a gold shield, has his own sign, does not use rings and jumping with 50 rings will turn you back into Supersonic
 
Play as Beta Supersonic - In options switch to "Sonic Alone" then do the level select code, then the debug and all chaos emeralds codes, at the beginning of the level create 50 rings and collect them, become Supersonic, then create two transfer boxes and hit one, now create something that hurts and lose your rings, now hit the other transfer box (Beta Supersonic is  invincible, has his own sign, does not use rings, getting speed shoes will sometimes slow you down after 20 seconds, getting invincibility will sometimes change you back into Gold Sonic after 20 seconds and jumping with 50 rings will turn you back into Supersonic
 
Easy Act End - In Debug find the thing that looks like jumble of metal, place it and jump on top, animals come out and you passed the act