Proto:Sonic CD (Sega CD)/Prototype 510

The earliest known prototype of Sonic CD, named because the CD dates itself to May 10, 1993. It was discovered by a group of fans called Sega Extreme in the summer of 2000.

Graphics

 * A SEGA logo, complete with the classic "SEGA" sound, is present at the beginning. It was removed from the final version.
 * 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.
 * Amy looks different, having larger eyes and quills.
 * Each Zone has its own unique type of flower.
 * The goal post in the prototype has a somewhat jollier Sonic. The final version re-drew Sonic's hand to be angled more toward his face:


 * The Exit selection in the Time Attack menu has a different graphic, depicting the Little Planet:

Gameplay

 * Only the first three Zones are playable in normal gameplay. After clearing Tidal Tempest, the game sends the player to a scrolling screen with the words "COMIN' SOON" and then the title screen. The "COMIN' SOON" 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.
 * 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.
 * Coming within range of the goal does not cancel the time warp.
 * The Special Stage 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.
 * This prototype featured 3 additional power-ups:
 * "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.
 * Destroying both of the robot transporters 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.

Title Screen
The title screen is very different:
 * The prototype refers itself as "CD Sonic the Hedgehog", as opposed to "Sonic the Hedgehog CD".
 * A gold emblem with the Sega logo and the copyright date (1993) is present, but was removed from the final version.
 * The prototype's title screen is 320*224, instead of 256*224.
 * The grass is much less pixelated and the mountain with Eggman/Robotnik's face was re-drawn to be taller.
 * The clouds are scrolling from right to left, instead of scrolling in a way that suggests sprite scaling.
 * Little Planet is much less detailed and more transparent.
 * There's a text string overlaid, showing who provided the vocals for "Sonic - You Can Do Anything", likely for press purposes.

Opening FMV
The opening video background is a layered brick background, with "SONIC" inscribed on each brick. Also under the FMV are the Japanese symbols "開発画面". They translate to "development screen".
 * The scene showing Little Planet chained to the ground is played in reverse.
 * The video in the prototype has a speed of 50Hz.
 * The final game added a scene from the mountains with Robotnik's face and the attached chain, but that's missing in the prototype.
 * The opening song glitches throughout, with some bugs and breaks during play.

Special Stage
The Special Stage is not yet playable, and a demo of it is accessible by waiting on the title screen.
 * During the demo, the text "The programmer has a nap. Hold out! Programmer!" will flash on the screen repeatedly.
 * There are no UFOs to destroy yet.
 * There are oil slicks present that were taken out in the final, becoming unused graphics. Through hacking, it turns out they are non-functional.

Music

 * The music is largely identical to the final Japanese/European version's soundtrack, although fade-outs are missing.
 * The title screen/time attack music is almost completely different in the prototype, with no resemblance to "Sonic - You Can Do Anything":


 * The Speed Shoes music is a different remix of "Sonic - You Can Do Anything":


 * The Special Stage theme is extended. It lasts 4 and a half minutes.
 * 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.
 * Pausing the game does not pause the music.

Sound Effects

 * Several object sound effects are missing from the prototype.
 * The jump sound plays at a lower pitch.
 * Destroying a badnik plays a different sound rather than the traditional badnik explosion sound.
 * The time warp sound is different, and is very grating on the ears:

Level Select
On the title screen, press Start on the second controller and then press Start 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 Start to enter it.


 * The level select screen skips from level 1 to level 3. The missing level 2 is known as R2 because it was missing in the PC version which stored the levels in R# folders.

Debug Mode
Press Start on the second controller at any time during gameplay to enable/disable Debug Mode.

Palmtree Panic

 * 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 it 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 they are lilac.

Collision Chaos

 * The beginning of the first two Acts are different.
 * At the beginning of Act 1, Metal Sonic is able to electrify Sonic.
 * 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.

Tidal Tempest

 * The water is a different color in all zones, the graphics are somewhat different.
 * Spike balls appear in fours.
 * The waterfall is much lower in this prototype.
 * A ripple effect is added to the foreground. Normally it's only present in the background.
 * There is no splashing effect when jumping in and out of water.
 * You cannot pause the game for some reason.

Quartz Quadrant

 * There are no rings.
 * A 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. The Sonic monitor was restored in the 2011 rerelease of Sonic CD, appearing in Act 3 instead.
 * The sky in the Good Future is black.
 * All the objects use the same sprites across all time zones, 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 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.

Wacky Workbench

 * There are no rings.
 * In the Present, the background has a green color scheme, while the final has more of a blue color.
 * The Past has a blue color scheme for the foreground. In the final, the foreground is bright green.
 * The Bad Future's background has a purple color scheme.
 * All three acts are missing objects across all time zones.
 * Tubes and tunnels do not work.
 * The electrical conduits cannot hurt you.
 * Sonic does not curl into a ball when he bounces off the floor.
 * The angel statue in the Past of Act 1 is a solid object and doesn't give you rings.
 * There is no boss in Act 3. The prison capsule is present, however.

Stardust Speedway

 * Act 1 has a crazy mixture of colors moving up and down in the Present.
 * The Good Future has a blue color scheme, and the background is blue and black.
 * The sky in the Bad Future is constantly flashing red.
 * All three acts have no objects or rings.
 * Act 2 has a slightly higher starting position.
 * In Act 3, Metal Sonic does not appear to initiate the race.
 * Amy does not appear at the end of Act 3, making the level impossible to complete.

Metallic Madness

 * There are no rings.
 * The background in the Past of Act 1 has a purple tint.
 * The first two Acts have several bottomless pits that were taken out in the final version.
 * There are several objects in this zone that were taken out of the final:
 * A trapdoor similar to the ones in Scrap Brain Zone from Sonic 1.
 * 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.
 * The starting positions in Act 2 and Act 3 are much higher up.
 * The conveyor belts and spinning wheels in Act 2 don't work. There are also small variants of the spinning wheels.
 * Turntables that transfer you into the background of certain areas 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.
 * The stage is cut off in the "Mini Sonic" maze as the Goal is at the same coordinates as this area.
 * Amy does not appear after defeating the final boss, and no ending sequence has been implemented yet.