This is a piece of Concept Art for the scrapped Sonic CD level Dubious Depths, Ridicule Root, or R2.
- 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.
- The music for the past appears to have been planned as CD-quality audio at some point — an early build featured a CD rendition of Palmtree Panic's past theme, which eventually leaked online. However, the composers eventually decided to play the past music on the Sega CD's internal sound chip. Contrary to popular belief, this wasn't done due to running out of disc space, but rather as a creative decision to give it a "cheaper" and "prehistoric" sound.
- 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 underground/dungeon zone named "Dubious Depths" (or "Ridicule Root" earlier in development) that would have been in between Palmtree Panic and Collision Chaos that would've had machinery, spike traps and giant fans. However, due to the music data not fitting into the CD-ROM of the game and the zone not matching Sonic's speed, 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 game’s files on a PC (under the name R2, or Round 2), early concept art◊, leftover enemy and boss sprites◊, its appearance in the ending sequence◊ and its present theme, which would be recycled as the default track in the "D.A Garden" menu in the Japanese/European release (the American release uses an instrumental version of Sonic Boom instead).
- The Updated Re-release was going to have two brand new levels: a Shifting Sand Land inspired by the scrapped Dubious Depths called "Desert Dazzle", and "Final Fever", a new True Final Boss that would've been unlocked if all the Time Stones are collected. However, these zone proposals were rejected by Sonic Team, who wanted the port to stay faithful to the original game, resulting in both stages being scrapped. 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. Desert Dazzle later became the basis for Mirage Saloon Zone in Sonic Mania. 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". Every other round, including the elusive "Round 2/Dubious Depths" (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 a scrapped idea in which the animals would attack Sonic, due to them mistakenly thinking he was Metal Sonic.
