- Doing It for the Art: Practically the reason this game was made in the first place, since the developers had so many great ideas that they couldn't put into the original.
- Executive Meddling: Shigeru Miyamoto was not exactly thrilled about the addition of story elements in the original game (in the form of an (optional) storybook about Rosalina's backstory) and requested the Dev team to scrap the plans they had for this game.
- Recycled Script:
- 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 Palette Swap and with the Cloud Flower instead of the Bee Shroom. The star's title even 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 Whomp King in the Throwback Galaxy reuses most of his original quotes, as a Mythology Gag.
- Urban Legend of Zelda:
- In the level "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. 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". 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!
- There were a number of prerelease rumors suggesting that Sonic the Hedgehog would be playable. They ultimately proved to be false, but Sonic got his own Galaxy-like game with Sonic Lost World.
- Viral Marketing: Signal transmissions. No direct ad pitch presented, simply gameplay footage.
- What Could Have Been: 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.
Trivia / Super Mario Galaxy 2