- Christmas Rushed: Spencer Nilsen's sound team was given a meager two months to compose an almost entirely new soundtrack for the game's American release. They were so pressed for time that they weren't even able to replace the Past songs, due to the more complicated programming involved (i.e., the tracks being directly coded into the game instead of being stored as ordinary CD audio tracks).
- Cowboy BeBop at His Computer: Amy Rose's name is changed to Princess Sally in the North American Sega CD manual, even though Amy looks and acts absolutely nothing like her. All subsequent releases reverted this change.
- Cross-Dressing Voices: In this game, Sonic is voiced by Japanese singer Keiko Utoku, who also does the vocals for the Japanese opening and ending themes.
- Cut Song:
- Cut segments of songs exist, as early prototypes had what appeared to be unused in-game music loop pieces that would apparently inconspicuously play while the CD track ends and re-loads from the beginning. May have been removed due to time or inability to perfect this feature, but it was restored in the 2011 remake.
- In the pre-release, the title screen and Speed Up tracks were totally different, and the Special Stage song had an extended cut.
- Within the CD audio tracks of the American version, there's a duplicate of the title theme.
- The Sega World 1992 prototype reveals that higher quality versions of the game's Past themes were going to be in the game, utilizing Red Book audio just like all of the Present and Future themes. This was dropped early on, and as such, the Past themes instead use utilize lower quality versions generated by the Sega CD's own PCM audio chip instead.
- Development Gag: During the Special Stages from unfinished pre-releases, a Engrishy message appears on the screen, telling the programmers to wake up and finish their jobs:The programmer has a nap!
Hold out! Programmer!
- Dummied Out: Aside from an eighth Special Stage, which can be accessed with a secret code, the most infamous cut content from Sonic CD is the elusive "Round 2", which was apparently a ruins stage. To fill in the void, "Desert Dazzle" was supposed to appear in the remake, but Sega declined the content and all that remains of it is a secret teaser picture. Christian Whitehead, the remake's developer, claims that this sprite sheet◊ was part of R2, which shows three unused enemies and a unused boss. There's also official concept art◊ of the level. Finally, a semi-complete layout of Desert Dazzle was left over in an updated release of the remake. The working Desert Dazzle design appears to have become the inspiration for Mirage Saloon Zone in Sonic Mania.
- Fan Nickname:
- Also counts as Refrain from Assuming, but "Toot Toot Sonic Warrior" is a common fan-name for the Japanese/European opening theme, "Sonic - You Can Do Anything."
- The secret Special Stage is sometimes referred to as "Eggman's Bathtub" due to the conspicuous giant Eggman face in the background combined with the heavy amount of water around the stage.
- Some fans have changed what "CD" stands for in the 2011 remake, such as "Completely Digital" or "Console Download".
- The cut ruins zone has no official name due to it being scrapped incredibly early in development, however it is generally referred to as "R2" (short for Round 2) by the fandom due to the games files listing it as such between R1 (Palmtree Panic) and R3 (Collision Chaos). Christian Whitehead's 2011 version of it is named Desert Dazzle, which has been adopted as a secondary name.
- First Appearance: This game marks the first of many appearances of Amy Rose and Metal Sonic.
- Flip-Flop of God: Sonic Team and Sega has shifted their position on the game's placement in the canon over time. Back in one 1993 interview, they implied that the game takes place between Sonic the Hedgehog and Sonic the Hedgehog 2, explaining the notable absence of both Tails and Super Sonic from the game. However, a decade later, and in another interview, they instead stated that the game took place after Sonic 3 & Knuckles, but before Sonic the Hedgehog 4, only to then re-clarify a day later that CD is a standalone adventure that doesn't have a concrete place in the canon, other than it took place before Sonic 4.
- Keep Circulating the Tapes: While Sonic CD itself has since become more accessible thanks to it's PC port in 1996, (which was also included in Sonic Gems Collection) and the remastered port by Christian Whitehead in 2011. The original Sega CD version has yet to see an official rerelease on any platform and copies of the original game tend to go up for extremely high prices on online stores. There were plans to include it in Sonic Mega Collection, however the lack of documentation for the Sega CD led to Sonic Team cutting it out from the lineup.
- Killer App: If it wasn't a reason to buy a Sega CD, it was one of the closest things it had to one.
- No Export for You: The Japanese/European version's soundtrack wasn't officially released in North America until the 2011 remake, which has both that soundtrack and the American version's, by members of the Sega Technical Institute. It was long rumored that licensing issues were holding back such a release, but Word of God has it that the remake almost didn't have the US soundtrack because of licensing issues.
- Orphaned Reference: One of the shots◊ in the ending animation features Sonic running through the scrapped R2 stage and narrowly avoiding an antlion, which was also scrapped.
- Promoted Fanboy: Whitehead, who did the downloadable remake. He was responsible for creating the Retro Sonic engine, a number of fangames, and is also a member of the Sonic Retro community.
- Screwed by the Lawyers: The vocals for the Japanese soundtrack were replaced with instrumentals for the HD remake due to unforeseen legal issues regarding the rights to them.
- Trope Namer:
- What Could Have Been:
- Naoto Ohshima originally wanted the time travelling to be done in real-time, inspired by Back to the Future; however, the programming team deemed this impossible and compromised with the Time Warp loading cutscenes in the final game. Ohshima believed that if Yuji Naka, known for his incredible coding skills, were developing CD instead of Sonic 2 at the time, it could have been possible.
- Fully-animated cutscenes that acted as transitions between stages were planned, but due to budget reasons, only the intro and both ending cutscenes were animated.
- Originally, there was a ruins level that would have been in between Palmtree Panic and Collision Chaos. However, due to dissatisfaction by the team and it not meeting quality standards, it was cut very early in development with the only traces of the zone left being Dummied Out leftover files discovered when going through the games files on a PC, early concept art◊, leftover enemy and boss sprites◊, its appearance in the ending sequence◊ and one of its tracks, which would be used as the default track in the "D.A Garden" menu.
- The Updated Re-release was going to have two brand new levels: "Desert Dazzle", inspired by Round 2, and "Final Fever". Time constraints, as well as Sonic Team feeling that it shouldn't deviate too much from the original game, resulted in both stages being cut. A glimpse of Desert Dazzle can be seen by entering "32" and "8" into the respective slots on the Sound Test menu (which, incidentally, also unlocks the level select for Tails), while half finished early attempts of the levels can actually be found in the games via hacking. Whitehead later released a hypothetical screenshot of Final Fever◊ as well as a description of how the level and boss battle would play out:Whitehead: Yeah, it's colourful since it was intended to be an all Time Stones boss (good future only). Time flows freely, and Eggman's machine is essentially invincible. The idea being Sonic can reach warp speed at any opportunity (instead of getting the warp posts) and must do so to "wind back the clock" to damage the boss. Some parts are running, some areas the screen is locked. I was slightly worried the idea of running to warp might not be self evident (no warp screen, the level and boss would change in real time with some neato effects).
- While Whitehead was still pitching the game's digital port, Simon "Stealth" Thomleynote began work on a port for the Nintendo DS, but the project was abandoned once Whitehead's pitch was accepted.
- One of the pieces of concept art for the final boss shows Eggman in a mech suit, though with the panels from the final design still present. This concept eventually became the basis for the final boss of Sonic Mania, the Phantom Egg.
- On October 26, 2019, a prototype of the game shown off at a Sega World event in 1992 was dumped online. Only Palmtree Panic Zones 1 and 2 are playable, then known as "Salad Plain" (possibly hinting that the rest of the titles would have used food puns rather than Alliterative Names). Every other round, including the elusive "Round 2" (notably this is the only known prototype to reference the level, meaning it was scrapped very early on), is listed in the Time Attack menu but is not present on the disc. There were two monitors that were cut from the final version: a Blue Ring monitor which basically acts as invincibility (in later builds, it acted like a triple-layered shield) and a Clock monitor that would stop time. Past themes were also seemingly going to use clearer Red Book audio like the Present and Future themes, instead of the Sega CD's own PCM audio chip. Finally, playing with a second controller would spawn a second, playable Sonic.
- According to Masato Nishimura, Wacky Workbench was originally titled "Crazy Toy Box".
- Also according to Nishimura, the Metal Sonic projections in the past zones are a leftover from an scrapped idea in which the animals would attack Sonic, due to them mistakenly thinking he was Metal Sonic.
Trivia / Sonic the Hedgehog CD