Sonic the Hedgehog Cheats

Drunk Sonic
During the demo, hold [C]. Sonic will crash into walls and get hit by enemies.

Level Select
At the title screen, press Up, Down, Left, Right. You should hear a noise like a ring being collected. Then, hold A and press Start for a level select!

Frame By Frame Motion
It doesn't matter when or where you use the code. While the game is paused, (I used a Virtual Console Controller) you can do three things.

Note: The game must be paused for this to work. I am not sure if the Wii Mote will do the same effects. On the Virtual Console Controller:

Y Button = A Button on Sega
A Button = B Button on Sega
B Button = C Button on Sega

Press and Hold [A]: Play In Slow-Motion
Press [Y]: This will reset the game to the title screen
Press [B]: Can Only Press Each Time. Will move onto the next frame

Unlock Different ending
Beat game with all chaos emeralds.

Glitch: Walk through walls in Marble Zone
When you ride the green block accross a sea of lave, there are a couple of big blocks in front of you with rings on. If you hold the D-PAD [Down] button, Sonic will crouch. The green block will go underneath the blocks, but sonic will remain on it, and pass through the walls. Note that this ONLY WORKS WHILE CROUCHING.