stage select
At act 1 in mushroom hill zone, go to the first push-pull lever near a speed sneaker monitor and a mad mole. Get on to the level and press l,l,l,r,r,r,u,u,u, and press start and then A. This should restart the game. Go back to the tittle screen and go to sound test.
stage select ( sonic 2)
AT tittle screen, press, u,u,u,d,d,d,l,r,l,r and then hold A and press start.
debug mode (sonic 2)
Enter the stage select trick and go to the sound test and play this in order, 1,9,9,4,1,0,1,8 and then highlight a stage and hold A and press start.
stage select (sonic 3)
Go to angel island zone and go to the first swinging vine and press l,l,l,r,r,r,u,u,u and press start and then A. Come back to the tittle screen and go to sound test.
debug mode(sonic 3)
Go to mushroom hill zone from your stage select and go to the first push and pull level near a speed sneaker monitor and a mad mole. Go on to it and press l,l,l,r,r,r,u,u,u and restart the game and go back to sound test and highlight the stage and hold A and press start.