Sega Master System Cheats - Sonic The Hedgehog Chaos

Level select:

Press Up two times, Down two times, Right, Left, Right, Left, 1 at the title screen.

Sound test:

Press Down two times, Up two times, Left, Right, Left, Right, 1 at the title screen.

Invincibility:

Select Sonic and press Up + [Jump] continously, then hold Up while in a jump. If done correctly, Sonic will glitter and be invincible until he stops running fast.