Level select:
Press Up(2), Down(2), Left, Right, Left, Right at the title screen.
Then, press 1 or 2 to select a new starting level.
Invincibility:
Select Sonic, then hold Up and continuously jump. Eventually Sonic will
begin flashing. Note: The invincibility will end when Sonic stops running.
Sound test:
Press Down(2), Up(2), Left, Right, Left, Right at the title screen.
Then, press 1 or 2 to enter the sound test screen.
