Sonic the Hedgehog

After the SEGA logo fully appears, tap the letters A, G, E, S in that order. The hidden credits screen will appear.

Start a new game on the "No Save Mode," and as soon as the SEGA logo fully appears, quickly tap the letters S-E-G-A in order. You should hear a ring sound if done correctly. Then hold down on the screen anywhere with both thumbs and continue to hold through the title screen and you will be taken to the hidden options menu.