- 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.
- Fan Nickname: The giant Lakitu boss in Yoshi Star Galaxy is the only boss never named in-game. Though the Prima guide calls him King Lakitu, he's commonly referred to as Giga Lakitu. Also Fiery Gobblegut for the rematch with Gobblegut in Battle Belt, and Whimps for the miniature Whomps that assist the Whomp King in his battle in Throwback Galaxy (named Pattan in Japanese).
- 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.
- Refitted for Sequel: Several mechanics and ideas that were scrapped from the first game are properly revisited here, Such as Yoshi and Starship Mario, both of which were originally intended for the first game, but were scrapped.
- 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! For the record...
- 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. They also were inexplicably privated from the Nintendo YouTube channel, leading them to become lost media for a period of time.
- 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.
- The team considered inserting cameos of characters from other Nintendo IPs into the game, such as characters from Donkey Kong and Pikmin, however, this was shot down by Shigeru Miyamoto.
Trivia / Super Mario Galaxy 2