* AllStarCast: In addition to the ''Anime/SonicX'' voice cast, they also have Creator/LaceyChabert voicing Princess Elise.
* {{Blooper}}:
** During Shadow's story, you can hear the voice actor for the G.U.N. soldier flub his line and repeat it again... and it's all unedited. Also, another G.U.N. soldier over Rouge's radio refers to the Scepter of Darkness as the "Book of Darkness" at one point, though the subtitles are correct.
** The very first quest in the game is called "The ''winder'' of a shoemaker". It's definitely a typo, and was probably supposed to be "wonder".
* BuryYourArt: The game hasn't seen a physical reissue since 2010 due to Sega deriding it as an ObviousBeta.
* CelebrityVoiceActor: Princess Elise was voiced by actress Creator/LaceyChabert, though she's still prolific in voice acting.
* ChristmasRushed: Sega wanted the game out in time for Sonic's [[MilestoneCelebration 15th Anniversary]], so Sonic Team was forced to rush it out the door and disregard bug testing and quality assurance. The final result was a game that left a black mark on the series and Sega's reputation forever, and one of the most infamous video games ever made.
* CreatorBacklash:
** Sega apologized on its multiple issues, and later [[http://www.segabits.com/?p=4766 pulled it from stores entirely]]. All as an effort to forget that the game existed, and to hope that this problem never happens within the series again. However, they weren't ''quite'' ashamed enough to write it out of Sonic canon forever, as several elements from this game appeared in later installments. Silver appears in a few later games like ''VideoGame/SonicRivals'' and one of the levels with a boss fight are in ''VideoGame/SonicGenerations'', albeit with a major gameplay overhaul.
** The official Website/{{Twitter}} account for ''Sonic the Hedgehog'' has made fun of the game [[https://twitter.com/sonic_hedgehog/status/608343347623796736 more than]] [[https://twitter.com/sonic_hedgehog/status/608822114368544769 once.]]
** During the [[https://m.youtube.com/watch?v=SChPv1Z-c0M 25th anniversary event]], all the Sonic games up to that point were listed and each game was given a cheerful description. When the list got to Sonic '06 its description was just the game's loading screen.
** Sonic makes reference to the game in ''VideoGame/LegoDimensions'', and makes it clear he'd rather forget about it.
--->'''Sonic:''' [[WesternAnimation/AdventureTime Lumpy Space Princess]], huh? Last time I met a princess, I— We... Y'know, I d-- I don't quite remember. Never mind.
** When Takashi Iizuka (the current head of Creator/SonicTeam) was asked about the infamous kiss between Sonic and Elise in the last story [[https://www.ign.com/articles/sonic-hedgehog-smooching-human-kiss-princess-elise in an interview]], he simply stated the following.
--->'''Takashi Iizuka:''' I don't think we'll be doing that again.
* DummiedOut: A number of features that were scrapped due to time or technical limits, some revived in later projects:
** An energy meter is displayed on the HUD when playing as Sonic/Elise, but it is only used for two levels, when Sonic is carrying the Princess. The meter has absolutely no use in the game since the skill which meant to consume it was never implemented. The various gems are meant to drain said meter when used, but they don't, making them very exploitable. It was probably meant to be used in Sonic's Dusty Desert, where he needs Elise's power to run on the hot sand unharmed.
** A power gem which allows transformation into Super Sonic during regular play ''a la'' the Genesis/Mega Drive games. This feature was later revived for ''VideoGame/SonicColors''.
** Whatever purpose the Medals of Soleanna served. For some reason, the Medals can still be picked up in the city and in action stages.
** Going by the [[AllThereInTheManual instruction manual]], it appears Tails and Omega would have had some limited flight ability which was measured by a gauge. Something similar to ''VideoGame/SonicAdventure2''[='s=] Chaos Drives would appear during levels, and something referred to as Light Cores would provide some sort of level-up mechanic. The latter was also revived for ''Unleashed''. Chaos Drives and Light Cores are actually still in this game: the former are dropped by robots, and the latter are dropped by Iblis and Mephiles' monsters. They refill the player's power meter, which was a concept revived for ''VideoGame/SonicGenerations''.
** Messages announcing the unlocking of stories/missions for the Amigo characters and Metal Sonic are in the game data.
* ExecutiveMeddling: During development, Sega execs rushed Sonic Team into developing the game in time for the Christmas season as well as ''Sonic'''s 15th anniversary.
* FirstAppearance: Of Silver.
* GodNeverSaidThat: The game is never referred to as a ContinuityReboot by Creator/SonicTeam at any point. Only that they wanted to make the game appeal to a wider audience and that they wanted to [[RevisitingTheRoots revisit the roots of the franchise]], which caused some to assume that it's a reboot, when it was never actually considered to be such. If anything, it's heavily implied that the game's events are ultimately canon to the rest of the franchise, as future Sonic games have mentioned and referenced the game's events in subtle ways and ''VideoGame/SonicGenerations'' outright features Crisis City as one of its zones (as well as a comment from Blaze stating that she finds the place to be familiar to her). That said, they've never explained why Blaze is suddenly in the future in this game as opposed to another dimension.
* KeepCirculatingTheTapes: While used copies aren't too difficult to find, Creator/{{Sega}} pulled all new copies from store shelves in 2010, on top of delisting it from the Xbox 360’s digital store that same year, so don't expect a rerelease in any form any time soon. Ultimately subverted, you can buy the game on the Xbox 360 store once more as of late May 2022...then double subverted when that storefront itself was announced to be shut down in 2024.
* ManualMisprint: Perhaps unsurprisingly, considering the game was released as an ObviousBeta. One example, though -- the manual states that the energy meter on the HUD is utilized in conjunction with the special gems that Sonic can buy at the shop in Soleanna, and that it is meant to drain with each usage of the gems. This is not true in the actual game; again, since it was released in an unfinished state, the energy meter never drains and as such Sonic is able to use the gems as much as he wants, when it is quite clear that it was never intended to be this way due to their abilities to break the game on unlimited uses.
* MedalOfDishonor: Meta-example; the game won the "Worst Game of the Decade" award over ''VideoGame/BigRigsOverTheRoadRacing'', and while ''Series/XPlay'' had ripped apart a few ''Sonic'' games prior and made their disdain for the franchise at the time known previously, this was the first Sonic game to get one of their "Golden Mullets", their version of the MediaNotes/GoldenRaspberryAward that was taken from ''Aquaman'' (the first game on the show to get a 1 out of 5 score).
* MilestoneCelebration: This was the main game released to celebrate 15 years of ''Sonic the Hedgehog''. The others being a port of [[VideoGame/SonicTheHedgehog1991 original game]] for the Platform/GameBoyAdvance, ''VideoGame/SonicRivals'' for the Platform/PlayStationPortable, and ''VideoGame/SonicRiders'' for the sixth generation consoles and PC.
* TheOtherMarty: Creator/VeronicaTaylor was the original choice to voice Elise before being replaced with Creator/LaceyChabert, but her voice can still be heard in early trailers.
* PromotedFanboy:
** Actress Creator/LaceyChabert, a longtime ''Sonic'' fan, voices Elise in the English version.
** Lee Brotherton, who sings "Dreams of an Absolution", got his start making music on Music/OverClockedRemix.
* StuntCasting: Elise is voiced by Creator/LaceyChabert, and was voiced by Creator/VeronicaTaylor in the promo trailer.
* TroubledProduction: Although the game, unlike ''X-treme'', was released, the final product was likewise ''[[ObviousBeta far]]'' from finished from the get-go. After Yuji Naka -- one of the founding members of the ''Sonic'' franchise and a longtime member of the Sonic Team ProductionPosse -- resigned from Sega and consequently left ongoing development of the game, massive pressure was then put on the game's director Shun Nakamura and the rest of the development team to have the game ([[ToughActToFollow which was supposed to be another great Sonic game that would be used to help re-launch the franchise on next-gen consoles]]) finished in time [[ChristmasRushed for that year's Christmas season]] as well as [[MilestoneCelebration be released before year's end to qualify as the 15th anniversary title]]. And then if that wasn't enough, the development team was split so that a new team could work on [[VideoGame/SonicAndTheSecretRings a new Sonic game for the Wii console]], the result of Sega discovering that a Wii version of the game (which was in development along with the [=PS3=] and 360 versions) was unfeasible due to the Wii's technical limitations. The fact that they had to develop two remaining console versions of the game at the same time during the short development process did not help matters. The final product was ravaged by reviewers and fans alike as one of the worst video games ever, and — contrary to popular belief — sold poorly (though for what it's worth, the 360 version still sold well enough to warrant a Platinum Family Hits reprint, but that probably didn't do much to help), which was enough to have some dire consequences of the franchise in its future, to say the least.
* {{Vaporware}}: There was originally meant to be a PC version, which was never released. A Platform/{{Wii}} version was also planned but abandoned in favor of ''VideoGame/SonicAndTheSecretRings''.
* WhatCouldHaveBeen: It was already a [[ObviousBeta mess of a game]], but it was only made worse by the fact that it looked promising at one point;
** Early trailers and demonstration videos promised things like [[InUniverseGameClock a day/night system]], multiplayer minigames, and a "free mode" that allowed you to play as any character without storyline constraints. Several functions described in the manual are ''not actually in the game'', including things like the implementation of the Action gauge (it is completely pointless for Sonic and is rather barebones for Shadow and Silver), [[EvolvingAttack "maturity" levels for Sonic's custom actions]] (there are none), and a flight gauge for Omega's hover ([[GameBreaker he can hover forever]], [[GoodBadBugs there is no gauge]]). Most depressingly, code was found for a purchaseable gem that allowed Sonic to relive his glory days of going [[SuperMode Super Sonic]] in-level, rather than [[EleventhHourSuperpower just for the final boss]]. Such a thing was never used until ''VideoGame/SonicColors''.
** There were originally plans to create a Wii port of this game, but hardware limitations had them make ''Sonic and the Secret Rings'' instead. Ironically, Sega taking half of '06's team to work on ''Secret Rings'' was a major contributing factor to '06's unfinished state.
** A more minor standpoint, but it was implied in some unused quotes in the game that Sonic/Shadow gets sucked into the tornado in Crisis City and the other one has to rescue them, the two nearly thanking each other. In other words, it was implied they were going to be playable in each other's action stages.
** There is an entire unused hub world with ''cars'' within the game, as well as 50 unused missions for various different characters and in various different states of completion.
* WordOfGod: Takashi Iizuka (who is currently head of Sonic Team but didn't work on ''06'') has stated Blaze does ''not'' originate from this game's dark future; Silver is from that future, but Blaze is still originally from the Sol dimension, as established in ''VideoGame/SonicRush''. When asked why she was in Silver's future at all, Iizuka gave it a {{Handwave}}, saying the two of them got [[EasyAmnesia amnesia]] "[[https://www.youtube.com/watch?v=9ATsyA-0Vq8&t=5627 as do everyone else]]". In other words, he's saying that the characters have forgotten it happened, so [[CanonDiscontinuity maybe fans ought to as well]].
* WordOfSaintPaul: One of the game's writers, Creator/ShiroMaekawa, has all but confirmed on [[https://twitter.com/mizuhano/status/1010563445068976128 Twitter]] the theory that the original intent for Silver's ending was that Blaze was returned to the Sol dimension (making this game a StealthPrequel to ''VideoGame/SonicRush''). Maekawa has also implied that Blaze still houses the power of Iblis inside her soul, and that she has "tamed" it to access Burning Blaze (hence why she briefly becomes Burning Blaze after absorbing it in Silver's ending). However, he admits that [[GodDoesNotOwnThisWorld Word of God likely sees things differently]].
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