* DummiedOut:
** Flying Mario and Ice Mario from the first game, only accessible via hacking. While the latter transformation files have to be imported from the first opus, the former is still fully functional. However, putting the Ice Flower and/or the Flying star into a level via an editor will freeze the game. This is because the Red Star and Ice Flower objects were removed despite being fully functional. With some patching of the game's code, the objects can be added back in.
** Many unused interactions in-game can still be found in the files.
** In an interview, producer Yoshiaki Koizumi mentions that a "Bone Mario" power-up was considered, but declined to go into detail. Unused code and text refers to the "Bone's Curse", which apparently involved Mario assuming a skeleton form that left him invulnerable to damage at the cost of collapsing into a pile of bones like Dry Bones. Mario's health would drain over time, and while stepping into light would restore him, it didn't remove the power-up effects (alternatively, Mario would go back to his skeleton form after stepping out of the light), implying that the power-up would be involved in levels where Mario would have to quickly and carefully avoid obstacles and keep himself alive.
* ExecutiveMeddling: Creator/ShigeruMiyamoto was not exactly thrilled about the addition of story elements in the [[VideoGame/SuperMarioGalaxy original game]] (in the form of cinematic sequences and an (optional) storybook about Rosalina's backstory) and requested the dev team to scrap the plans they had for them in this game.
* MilestoneCelebration: The game was released during the 25th anniversary year of ''VideoGame/SuperMarioBros1''.
* RecycledScript:
** One secret star in the Puzzle Plank Galaxy involves you fighting Bugaboom in the exact same way you fought him in [=SMG1=], only with a PaletteSwap and with the Cloud Flower instead of the Bee Shroom. The star's title even [[LampshadeHanging lampshades this]] with its title, "Bugaboom's Back". Also, there's a boss rush mode later on in the game involving other [=SMG1=] bosses.
** The [[spoiler:[[VideoGame/SuperMario64 Whomp King]] in the Throwback Galaxy]] reuses most of his original quotes, as a MythologyGag.
* RefittedForSequel:
** The game started as an expansion for the [[VideoGame/SuperMarioGalaxy first game]] that they made into its own game because they had so many ideas. [[HistoryRepeats A similar situation]] occurred roughly a decade later with ''VideoGame/TheLegendOfZeldaBreathOfTheWild'' and [[VideoGame/TheLegendOfZeldaTearsOfTheKingdom its sequel]].
** Several mechanics and ideas that were scrapped from the first game, such as Yoshi and Starship Mario, are revisited and realized here.
* UrbanLegendOfZelda:
** In the level "[[HailfirePeaks Shiverburn Galaxy]]", if you look closely, there is a texture of 3 shadowy figures against the sky texture. They're always visible, and always in the same location relative to Mario. [[NothingIsScarier Nothing in the game ever refers to them.]] In the game's code, the sky texture for that level is called "Beyond Hell Valley" and the texture with the shadowy figures is called "Hell Valley Sky Tree". [[{{Bowdlerise}} Some theories say that in the Japanese version of the game, Shiverburn Galaxy is called Hell Valley]], while others say that Hell Valley was a scrapped beta level. {{Creepypasta}} fuel ahoy! [[labelnote: For the record...]]Hell Valley is not the Japanese name for Shiverburn--it roughly translates to "Frozen Lava Galaxy". Nor is Hell Valley a scrapped level at all; in fact, Hell Valley seems to just be the internal code name for the decidedly-used Shiverburn Galaxy, as most other assets associated with the galaxy also use this moniker. It's generally assumed Hell Valley was just the working title the developers used before actually naming the galaxy. As for ''why'' the figures are there, that's still a mystery.[[/labelnote]]
** There were a number of prerelease rumors suggesting that Franchise/SonicTheHedgehog would be playable. They ultimately proved to be false, but Sonic got his own ''Galaxy''-like game with ''VideoGame/SonicLostWorld''.
* ViralMarketing: [[https://www.youtube.com/playlist?list=PL1E101C2470BE7ED9 Signal transmissions]]. No direct ad pitch presented, simply gameplay footage. They also were inexplicably privated from the Nintendo [=YouTube=] channel, leading them to become lost media for a period of time.
* WhatCouldHaveBeen:
** It's true that Mario games aren't known for their plots, but it would have been interesting to see where the dev team was planning to go with their story ideas, had they been given the chance.
** The team considered inserting cameos of characters from other Nintendo [=IP=]s into the game, such as characters from ''VideoGame/DonkeyKong'' and ''VideoGame/{{Pikmin}}''. However, [[ExecutiveMeddling this was shot down]] by Creator/ShigeruMiyamoto.
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