|title=Sonic the Hedgehog CD (prototype 510)
Sonic the Hedgehog CD prototype 510, referred to as CD Sonic the Hedgehog on the title screen, is the earliest known prototype of the game Sonic the Hedgehog CD for Mega CD produced May 10th, 1992. This prototype features a prominent "Comin' Soon" screen. It was 'discovered' by a group of fans called Sega Extreme in the summer of 2000. The game contains all the stages of the final game, but in a normal playthrough the player can only play the first three: Palmtree Panic, Collision Chaos and Tidal Tempest. The rest can be viewed through the Level Select. This prototype contains several differences from the final game.
"S" Monitor: Sonic has increased speed and an invincibility shield. It has a red "S" symbol.
Blue Ring Monitor: Functions identically to the "S" Monitor. Has an image of a blue ring.
Clock Monitor: Has an image of a clock. This does not work correctly, but its role was to freeze time for a few seconds. It does however stop the spinning of rings and the movement of objects aside from Sonic.
Badniks are not disabled in Good Future variations.
After completing the first 3 levels, a screen that says "COMIN' SOON" is displayed.
Code is in place for saving data, but only in Time Attack mode at this point.
It is possible, using the second controller, to control a second, "virtual Sonic" in gameplay. Whether this is for debugging purposes or an early 2 player prospect is unknown.
Tracks 2 to 24 and 32 are the same, but without fadeout.
Track 25 and 26: Early version of the title song, very different from the final version. It is a shortened version of Sonic - You Can Do Anything.
Track 28: Super Shoes song. A rather strange remix of "Sonic - You Can Do Anything".
Track 31: Special Stage song. It is longer than the original. It lasts 4 and a half minutes, and is considerably more "remix" than the original.
Several object sound effects are missing from the beta.
The home video is transmitted on a screen in a fund brick. Each brick has the name SONIC inscribed on it.
Also under the screen are the Japanese symbols 开発画面. They translate to development screen.
The showing Little Planet chained to the ground is played in reverse.
The video in the beta has a speed of 50Hz.
A scene from the mountains with Robotnik's face and the attached chain is shown, but is not included in the final version.
The Opening Song glitches throughout, with some bugs and breaks during play.
Only a demo of the special stage including the text "The programmer has a nap. Hold out! Programmer!" is accessible in a normal copy.
The only three special stage backgrounds in this version are Time Stones 2, 3, and 4 from the final game.
In a hack by SegaLoco which enabled controls in this special stage demo, it was found that the oil slick object is non-functioning and that there is no goal in this version of the special stage.
Amy acts differently than in the final. She will still latch on to you if you run past her, but if you stand still, she also just stands there. (In the final she latches on even if you stop.)
This is the only level where you can find the 3 unused monitors.
There is a section of a tunnel that appears in the final game, but not in the beta.
There is a section of a trunk in a waterfall, which does not appear in the final version, and there's also a section of a tunnel in the final game, which is in prototype but is inaccessible.
In the tunnel, Sonic is not wound to enter, and cannot leave through the other opening. Therefore, Sonic must enter the tunnel at top speed to leave through the other opening. In a secret tunnel, Sonic walks horizontally to climb.
In the Bad Future of Zone 3, if Sonic is launched by a spring at the beginning of the level, it gets out of focus and the same scenario sticks in the same position.
The palm trees of the Bad Future of Zone 3 have the same appearance of the palm trees of the Good Future.
The EGG-HVC-D01 in the prototype has a different design. The robot is entirely gray, the feet are flat with sharp edges, and have pincers rather than the shields from the final version. In the Bad Future, parts of the robot are red, while in the Good Future it is lilac.
An Extra Life monitor can be found at the very beginning of Act 1 Good Future. This doesn't appear in the final. In both prototype 510's Bad Future and the final version's Bad Future there is an Robotnik monitor in the same position. The extra life monitor was restored for the 2011 re-release of Sonic CD.
In Zone 3, Metal Sonic does not appear to initiate the race.
The Level Select screen
Level Select: On the title screen, press on the second controller and then hit on the first controller. A black screen with a list of numbers and letters corresponding to various levels and events appears. Make a selection and press to enter it.
Debug Mode: Any time during gameplay, press on the second controller.
: Toggle normal and debug mode
: Advance forward through the debug object list
+ : Advance backwards through the debug object list
: Place the selected object at the current coordinates