Proto:Sonic CD (Sega CD)


 * Warning, as there are still people fooled by this: the so-called "409" prototype is actually a hoax created by Sonic fan scene member Nemesis.

Prototype 712

 * Time Attack screens are up to date, but selecting a level in Time Attack locks up the game.
 * The Oil slicks are present but don't affect game play in the Special Stage.
 * The Special Stage demo found by waiting at the Title Screen isn't a demo at all; it is fully controllable.
 * The starting point for all Special stages is on the far corner on the dirt that slows you down, instead of starting on the road.
 * The time monitor when placed with the Debug mode causes other monitors to stop blinking.
 * The blue ring monitor is now used like a ring shield, You can take 2-3 hits without losing rings.
 * Getting All Time Stones doesn't change all futures to good.
 * When you gain an extra life, instead of Sonic saying "Yes", he says "Yeah".

The RAM save screen has very different visuals.

Prototype 920
A U.S. pre-release with the original Japanese/European version soundtrack. It has the addition of the updated copyright on the title screen and the level-restart code seen in the U.S. final.