Sonic CD was a video game released on the SEGA Genesis add on, the Mega CD/SEGA CD. Sonic CD is still highly acclaimed by Sonic fans. Oddly, Yuji Naka never took part in its development, but instead was helped by Sonic creator Naoto Ohshima. This game introduces us to Amy Rose and Metal Sonic for the first time.
A few years after the console release, the game was ported to PC and was also included in Sonic Gems Collection. In December 2011 it was ported again for XBLA, PSN and mobile platforms, the release containing relevant achievement and trophie support, the addition of Tails as an unlockable character and the option to select between the original Japanese soundtrack or the American sound track.
Sonic, followed by Amy, races to Never Lake in order to see the Little Planet, a mysterious planet which only ever appears over Never Lake in the last month of the year. Sonic has heard about the planet and it's Time Stones which are said to be able to manipulate time itself. However, once they reach the lake, they see the planet isn't as it should be, instead of trees and bright flowers, it's covered with rocks and sand, and is tethered to a rock by a giant chain. Just as they are looking up at the planet, Amy is kidnapped by Metal Sonic leaving Sonic no choice but to go after her, and also stop Dr. Robotnik who is in the process of converting the planet into a giant fortress.
The game's physics have Sonic feeling generally more sluggish than normal. His spindash in Sonic CD is different than that of Sonic the Hedgehog 2; the position he takes in both games is different. A new move was added to complement the Spin Dash: the Super Peel Out.
 Past and Future
The game's key element is the concept of time travel. The player can travel to four different versions of each level in three different time periods, starting in the Present for the first 2 acts, and the future for act 3. Time travel is accomplished by "Past" or "Future" speed posts scattered around the levels. There are never any "Past" signs in the past and never any "Future" signs in the future.
The past shows the time before Dr. Robotnik has taken over. The future shows what happens when Dr. Robotnik's plan progresses. These changes might effect the amount of enemies in each stage or various obstacles such as loops and trampolines. Use the Past and Future system to your own advantage.
In the Past of each Act there is a machine hidden in the level that if found and destroyed in each act will give a Good Future in Act 3 where you fight Dr. Robotnik. A Good Future is a future for that zone that is free from Dr. Robotnik's influence, whereas a Bad Future is, obviously, one that has been devastated by him. Collecting all the Time Stones will ensure a Good Future for all zones.
- Sonic the Hedgehog
- Amy Rose
- Dr. Robotnik
- Metal Sonic
- Miles "Tails" Prower - in the 2011 re-release on Xbox 360, Playstation 3 and Mobile platforms, Tails features as an unlockable character. Tails does not feature in the original versions.
- Palmtree Panic Zone
- Collision Chaos Zone
- Tidal Tempest Zone
- Quartz Quadrant Zone
- Wacky Workbench Zone
- Stardust Speedway Zone
- Metallic Madness Zone
- Special Zone
- Bobbin Walker (EGG-HVC-001)
- Pinball Machine
- Bubble Shield Blaster
- Mine-Dropping Conveyor Belt
- Rocket Mobile
- Metal Sonic
- Final Fever
If you let Sonic sit for three minutes without doing anything, he'll grow bored, say "I'm outta here!" and race off the screen, thus resulting in a GAME OVER.
There are 2 endings in Sonic CD, determined by whether you finish the game with all the Time Stones or not.
After finishing Metallic Madness Zone and defeating Dr Robotnik you are treated to a short animation of Sonic, with Amy, escaping the destruction of Robotnik's influence on the Little Planet. Sonic leaves Amy and runs off, watching the Little Planet break away from the chain that ties it to the ground, the planet begins to glow in the image of either Sonic (if you finished the game with all the Time Stones) or Dr. Robotnik (if you missed any Time Stones). Then the planet pulls into the air and explodes, scattering sparkles if you finish the game with the Time Stones.
Then the credits roll, along with more animation on Sonic travelling through the zones. Once the credits have finished there is one of two small endings. If you finished with all the Time Zones, the sparkles that fall from the Little Planet fall to the ground and flowers grow. But if you missed any Time Stones, the Little Planet reappears, chained to the ground.
 Cheat Codes
From the title screen, press Down, Down, Down, Left, Right, A to call up a Sound Test menu. Special things will happen if you select the following sound combinations and press Start.
 Debug Mode
FM40, PCM12, DA11
 Special Stage Selection
FM07, PCM07, DA07
 Level Select
At the title screen, press Up, Down, Down, Left, Right, B. Strangely, this code will only work once at a time- completing a level returns you to the Sonic CD title screen.
Music from the game features in the following CD soundtracks: