Sonic the Hedgehog CD is a 1993 platform game for the Sega CD. The story follows Sonic the Hedgehog as he attempts to save an extraterrestrial body, Little Planet, from Doctor Robotnik. As a Sonic the Hedgehog series platformer, Sonic runs and jumps through several themed levels while collecting rings and defeating robots. Sonic CD is distinguished from other Sonic games by its time travel feature, a key aspect to the story and gameplay. By traveling through time, players can access different versions of stages, featuring alternative layouts, music, and graphics.
The Sega CD’s flagship game, Sonic CD was conceived as an enhanced port of Sonic the Hedgehog 2, but was reworked after lackluster sales of Sonic 2 in Japan. Sonic co-creator Naoto Ohshima directed and Sega developers designed the game to show off the technical capabilities of the Sega CD. The game features the debuts of Amy Rose and Metal Sonic, and includes animated cutscenes produced by Toei Animation. Two soundtracks were composed for the game: the original score was composed by Naofumi Hataya and Masafumi Ogata, while the North American score was composed Spencer Nilsen, David Young and Mark “Sterling” Crew.
Sonic CD is often called one of the best games in the Sonic series and the platform game genre. Reviewers praised its exceptional size, music, and the time travel feature, although some also believed the game did not use the Sega CD’s capabilities to its fullest. It sold over 1.5 million copies, making it the Sega CD’s bestseller. The game was ported to Windows as part of the Sega PC brand in 1996, and to PlayStation 2 and GameCube as part of Sonic Gems Collection in 2005. A remastered version, developed by Christian Whitehead using the Retro Engine, was released for various platforms and mobile devices in 2011.
Sonic CD is a side-scrolling platform game similar to the original Sonic the Hedgehog. Players control Sonic the Hedgehog as he ventures to stop his nemesis Doctor Robotnik from obtaining the magical Time Stones and conquering Little Planet. Like previous games, Sonic can destroy enemies and objects (such as certain walls and television monitors containing power-ups) by rolling into a ball, and collects rings as a form of health. Sonic can also perform a “spin dash” and a “super peel-out” that can increase his speed. The game is split into seven levels called rounds; each round is split into three zones, the third of which culminates in a boss fight with Robotnik. Players start with three lives, which are lost when they suffer any type of damage without rings in their possession; losing all lives results in a game over.
Sonic CD is differentiated from other Sonic games through its time travel game mechanic, which allows players to access different versions of stages set in the past, present and future. Sonic starts the first two zones in the present, and can travel through time by hitting signs labelled “past” or “future” and maintaining speed for several seconds. By default, future stages depict neglect and decay after Robotnik has conquered Little Planet. Players are encouraged to convert each zone into a “good future”, with bright colors, no enemies, and few obstacles. To achieve a good future in each zone, players must travel to the past—a primitive, overgrown landscape—and destroy a hidden transporter where enemy robots spawn. Achieving a good future in every zone unlocks the best possible ending. The third zone is always set in the future, its timeline dependent upon whether the player destroyed both transporters.
By finishing a level with more than 50 rings, Sonic can access a special stage, in which he must destroy six UFOs in a pseudo-3D environment within a time limit. Time is reduced swiftly if the player runs through water, though a special UFO which appears when time is running out grants extra time if destroyed. If the player destroys all the UFOs before the time runs out, they earn a Time Stone. Collecting all seven Time Stones automatically creates a good future in every zone, and unlocks the best ending. The game also features a time attack mode, where players can replay completed levels in the fastest time possible; a “D.A. Garden”, where players can listen to the music of completed zones; and a “Visual Mode”, where players can view the opening and closing animations. The game also includes a save feature, which uses the back-up memory of the Sega CD.
Set between Sonic the Hedgehog (1991) and Sonic the Hedgehog 2 (1992), Sonic CD opens with Sonic journeying to Never Lake, where an extraterrestrial body, Little Planet, appears in the last month of every year. Sonic’s nemesis Dr. Robotnik has tethered the planet to a mountain and begun transforming it into a giant fortress with his robot army. Robotnik seeks the Time Stones, seven jewels capable of altering the passage of time. Sonic ventures into the planet, followed by the besotted Amy Rose, his self-proclaimed girlfriend. Robotnik dispatches his top robotic enforcer, Metal Sonic, who kidnaps Amy to lure Sonic into danger. Sonic clashes with Robotnik and Metal Sonic and uses time travel to stop Robotnik.
After racing and defeating Metal Sonic in Stardust Speedway and saving Amy, Sonic fights and defeats Robotnik in his base. Two endings exist, depending on whether or not the player collected the Time Stones or achieved a good future in each level. In one ending, Little Planet is returned to its rightful state and leaves Never Lake; in the other, Little Planet leaves Never Lake, but Robotnik uses the Time Stones to retake it and the player is urged to try again and free Little Planet forever.