Twisty Trials Galaxy in World S has an area which is the exact same as an area in Super Mario Sunshine. The level "Spinning Spinning and Spinning," is the same as the trial area in "The Secret of Ricco Harbor".
When you collect x777 or x7777 starbits and talk to the Captain he will say "Hey, you have 7777 starbits! How Lucky! Also if you have x9999 starbits he will say "What happens when you get 9999 starbits? Something nice I bet!
It is possible for Mario to get a Game Over during the game's closing credits. Finishing the game with 120 stars, a Bee Mushroom will appear in the Tall Trunk section of the credits. Collecting it and flying to the right in the Freezy Flake section of the credits, it's possible to get enough height to bypass the top boundary, thus resulting in a Game Over. The credits will roll, but are invisible behind a black screen.
The model for HellValleySkyTree makes an appearance in Grandmaster Galaxy, since the background from Shiverburn Galaxy was reused in this stage.
The Japanese, European and Australian versions of the game came packaged with an instructional DVD manual, explaining the basic controls, as well as showing advanced play. It was made because Super Mario Galaxy 2 would be more challenging than its predecessor. It's unknown why a DVD was never packaged for the American release.
The Diggas seen in the E3 2009 Trailer had a different design than those found in the Spin Dig Galaxy in the final version. Their eyes were positioned on their sides, rather than on top, and their bodies were rounder, making them look more like yellow Bullet Bills.
The Boss Megahammer was at one point called Mallettoid, and was referred to as such in demos.
Inside the game's files is an unused animation for King Lakitu. It shows him being hit so hard that his glasses fall off, causing him to search his face for them. However, the animation appears unfinished, as his fingers do not move, and his expression does not change.
Yoshi can be found at Bowser's Galaxy Generator. If you successfully bring him to the end, he will wave goodbye to you as Mario goes up the flag.
Super Mario Galaxy 2's internal disc ID is titled "Super Mario Galaxy More". This could suggest that Nintendo originally made the game as an expansion pack, rather than a true sequel.
Super Mario Galaxy 2 was the most pirated Wii game for 2 years running (2010-2011) with over a million downloads each year.
Yoshi's house can be found in World 1, Sky Station Galaxy. If you select the first mission and go up to Yoshi's house, there will be a sign in the front that reads: "Hello, friend! Please go around back! -Yoshi" If you then quit the level and then select the third mission and read the sign, it will read: "Hello, friend! Please go around back! -Yoshi the space dragon"
There is a level called the Throwback Galaxy. This level is the same as Whomp's Fortress from Super Mario 64 with a few changes and improved graphics. In the level, a Bob-omb Buddy mentions that Mario looks familiar, most likely referencing that he remembers him from Super Mario 64.
In the beginning of Shiverburn Galaxy, you can see odd, alien figures in the backgound. The name of the image in the game's files is "HellValleySkyTree."
When asked how Yoshi could survive in space, producer Yoshiaki Koizumi stated, "Well, it's because he's a space Yoshi!"