subdirectory_arrow_right Sonic The Hedgehog (Franchise)
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The Japanese manual for Sonic & Knuckles alludes to the game's Special Stages in its story section, which includes a moment where Sonic gets sucked through a Super Ring and arrives at the Master Emerald Alter, where the player accesses the Special Stages in the game. However, writer Ian Flynn would later claim the Special Stages seen throughout the series are not considered canon, instead only existing as a gameplay mechanic.
Ian Flynn statement:
https://www.youtube.com/watch?v=oKQNTyGQrCE#t=2230s
Japanese manual translation (page 12 in the manual):
https://info.sonicretro.org/File:S%26K_MD_JP_manual.pdf
https://web.archive.org/web/20151220201009/http://www.sonic-jam.org/sisghzs:md-sonick-t1
https://www.youtube.com/watch?v=oKQNTyGQrCE#t=2230s
Japanese manual translation (page 12 in the manual):
https://info.sonicretro.org/File:S%26K_MD_JP_manual.pdf
https://web.archive.org/web/20151220201009/http://www.sonic-jam.org/sisghzs:md-sonick-t1
subdirectory_arrow_right Sonic the Hedgehog (Game)
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Connecting Sonic & Knuckles to the first Sonic the Hedgehog will not allow you to play as Knuckles in the latter game. This was not due to hardware limitations as is commonly believed, but rather because the game's development team felt that, while Sonic 2 was designed with Super Sonic's flight in mind and thus had verticality to its levels fit for Knuckles' climbing, Sonic 1 was not, and therefore simply was not fun to play as Knuckles in.
subdirectory_arrow_right Sonic The Hedgehog (Franchise)
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Thrash design origins:
https://web.archive.org/web/20151102123335/http://www.bumbleking.com/forum/viewtopic.php?t=2220&postdays=0&postorder=asc&start=75
"Sonic Universe 3: Knuckles Returns" graphic novel
"Sonic Universe" Issue #11:
https://readcomiconline.li/Comic/Sonic-Universe/Issue-11?id=21631#1
"Sonic the Hedgehog" Issue #244 (Part Two of the "Endangered Species" arc):
https://readcomiconline.li/Comic/Sonic-The-Hedgehog/Issue-244?id=20223#1
Ian Flynn statement:
https://www.youtube.com/watch?v=Aju-OccReIw#t=993
https://web.archive.org/web/20151102123335/http://www.bumbleking.com/forum/viewtopic.php?t=2220&postdays=0&postorder=asc&start=75
"Sonic Universe 3: Knuckles Returns" graphic novel
"Sonic Universe" Issue #11:
https://readcomiconline.li/Comic/Sonic-Universe/Issue-11?id=21631#1
"Sonic the Hedgehog" Issue #244 (Part Two of the "Endangered Species" arc):
https://readcomiconline.li/Comic/Sonic-The-Hedgehog/Issue-244?id=20223#1
Ian Flynn statement:
https://www.youtube.com/watch?v=Aju-OccReIw#t=993
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In the Flying Battery Zone Act 1, there's an object known as "The Flying Battery" which can only be seen by taking a certain path. It's simply an obstacle that can be pushed and only appears once in the game.
subdirectory_arrow_right Sonic the Hedgehog 3 (Game)
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Game Informer article:
https://www.gameinformer.com/b/features/archive/2016/10/10/how-sonic-the-hedgehog-3-became-two-games-sonic-and-knuckles-lock-on-technology.aspx
McDonald's Sonic the Hedgehog 3 Happy Meal sweepstakes commercial:
https://www.youtube.com/watch?v=X4z6S6SErYA
Wikipedia article:
http://en.wikipedia.org/wiki/Sonic_the_Hedgehog_3#Development
https://www.gameinformer.com/b/features/archive/2016/10/10/how-sonic-the-hedgehog-3-became-two-games-sonic-and-knuckles-lock-on-technology.aspx
McDonald's Sonic the Hedgehog 3 Happy Meal sweepstakes commercial:
https://www.youtube.com/watch?v=X4z6S6SErYA
Wikipedia article:
http://en.wikipedia.org/wiki/Sonic_the_Hedgehog_3#Development
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