Sonic the Hedgehog CD 712 is a prototype of Sonic CD for the Mega CD.
Differences
• The RAM data screen is different. • Time attack screens are up to date but selecting to play a level in Time ATK 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 causes other monitors to stop blinking. • Blue Ring Monitor is now used like a ring shield, You can take 2-3 hits without losing rings. • Getting All timestones doesn't change all futures to good. • When you gain an extra life, instead of Sonic saying "Yes", he says "Yeah".
Some info taken from SonicRetro.
