Unlimited lives:
Press Left, Right, Down, A, and hold Start when Sonic appears from the
hole during the opening sequence. Keep holding Start until game play begins.
Level select:
Press Up(2), Down(2), Left, Right, Left, Right at the title screen.
View any level:
Press Up, Down, Left, Right, then hold A and press Start at the start
screen.
Bonus life:
Reach the end of any level with less than fifty rings. Enter the
turnstile, then stop and jump directly upward. If timed correctly, the
turnstile will stop spinning while it is off-screen. An extra life will appear
when Sonic lands back over the turnstile.