|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 on 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.
The menu is top-down with only "New Game" and "Time Attack" available.
Also appearing in the credits is Keiko Utoku, the singer in the Japanese and European Opening, likely for press purposes.
In the Time Attack screen, the exit logo displays an image of the Little Planet and the chain attaching it to the mountain with Robotnik's face
Sonic sports a different appearance on the Signpost.
Amy Rose has larger eyes and quills.
Each level features a different type of flower.
Title cards have "CD SONIC THE HEDGEHOG" instead of "SONIC THE HEDGEHOG CD".
The lives counter is slightly higher than normal, and there are no zeros in the SCORE and RINGS counter.
Active time warps are not indicated on the HUD.
This prototype featured 3 additional power-up Monitors:
"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.
The Giant Ring appears at the end of an Act regardless of how many rings you have collected, but it doesn't work properly yet, and entering it will not take you to the Special Stage.
After completing the first 3 levels, or after getting a Game Over, a screen with a scrolling marquee that says "COMIN' SOON" is displayed before returning to the title screen. This screen is still present in the final version, but is only accessible through the level select.
Code is in place for saving data, but only in Time Attack mode at this point.
Save data made by this prototype uses the filename "CDSONIC0000" instead of "SONICCD__xx", and is incompatible with later prototypes and the final.
Name entry is not yet possible in Time Attack mode.
The camera is locked for the first couple of seconds after the title card disappears.
You cannot control your momentum if you jump from a roll, which is normally the case in the Genesis games. This was changed in later prototypes and the final.
Coming within range of the goal does not cancel the time warp.
The time warp sequence cannot be skipped by pressing yet.
Destroying both of the robot teleporters in the Past does not change the future in Act 3 to a Good Future.
The game-ending "I'm outta here!" Easter egg does not work properly. The camera will follow Sonic as he jumps off the stage, and he'll die from a bottomless pit, losing a life and restarting the Act instead of causing an instant Game Over.
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.
The Past stages all play the music from the Present, as their own tracks have not been implemented yet.
The Invincibility and Speed Shoes monitors do not play their respective music.
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, star-shaped bushes and foreground pipes in both Futures of Act 3 are early designs and haven't been updated to match the Futures of the first two Acts yet.
The EGG-HVC-001 in this prototype has a different design. The robot is entirely gray, the feet are flat with sharp edges, and has 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.
The beginning of the first two zones are different.
In the beginning of Zone 1, Metal Sonic is able to electrify Sonic.
The yellow cups do not function properly yet. They'll catch Sonic, but he won't get sucked inside and will simply freeze there, playing the last animation he was in prior to touching it (jumping or running) until he is freed. The cups won't earn you any points yet, either.
The glass bumpers don't have a breaking animation yet and won't award any points for breaking them.
A strange group of three spinning teleporter-like objects that don't appear in the final can be placed with Debug Mode. When Sonic jumps into one, he freezes in place and they light up, then he teleports to another object in the group.
After landing the final hit on the boss, you have to wait for Eggman to leave the machine and fly away before you can advance.
A computer monitor showing Sonic's face 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 Eggman monitor in the same position. This Sonic monitor was restored for the 2011 re-release of Sonic CD, appearing in Act 3 instead.
There are no rings.
The outdoor background in the Good Future has a different palette. The sky is black, the mountains are darker, and the foliage is less refined.
All objects use the same sprites across all timezones, appear slightly different from the final, and have incorrect palettes.
The conveyor belts were intended to be controlled by standing on buttons, but they don't do anything.
Breakable walls cannot be destroyed.
The collision is wonky in some places.
Act 2 is devoid of objects in the Past and both Futures, and some of the tubes don't work.
Act 3 is also missing objects, and there is a string of different item monitors before the boss room.
The spikes that appear behind you during the boss fight have very basic sprites in both Futures.
Two shifting platforms with spikes by their sides found in tight corridors.
A set of platforms that behave like scales. They shift according to Sonic's weight.
A type of crusher that has a hole underneath that comes in a row of four. They push Sonic into the ground instead of crushing him.
Collapsing platforms have different graphics.
The starting positions in Acts 2 and 3 are much higher up.
The conveyor belts and spinning wheels in Act 2 don't work yet. There are also small variants of the spinning wheels that are taken out in later prototypes.
Turntables that transfer you behind iron curtains in Act 2 are missing.
Many objects are missing in the second half of Act 2.
The shrink/growth lasers (placeable with Debug Mode) have a delay before firing each laser. In the final, they are constantly firing.
Act 2 is cut off in the "Mini Sonic" maze, as the Goal is at the same coordinates as this area.
Act 3 has a different layout and glitched bumpers.
The iron curtain in Act 3 is covering the turntable and spiked wall when it shouldn't.
The background in the final boss arena is different in both Futures.
Amy does not appear after beating the final boss, and no ending sequence is implemented.
The Level Select screen
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.
Note that you will be taken back to the title screen upon completion of the selected level or upon attempting time travel.
At any time during gameplay, press on the second controller to enable/disable Debug Mode.
: 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.