Instead of just pressing A + B at the main menu of the demo, press and hold 1 + 2 when pressing A + B to access two additional stages.
UnlockablesHidden CharacterGet all 120 stars. Return to Rosalina on the Comet Observatory and request to fight Bowser again. Finish the credits and you will get a message saying that Luigi is now playable.
Grand Finale Galaxy and Star 121To unlock the final star and galaxy, collect all 120 stars with Luigi and beat Bowser. Doing so unlocks the Grand Finale Galaxy, which is the Star Festival seen in the beginning of the game. Collecting the 100 purple coins in this galaxy gets you the final star.
Unlock LuigiCollect all 120 Stars then go back to Rosalina at the Comet Observatory and fight Bowser again. Luigi will be unlocked as the main character after the credits.
Hints, Tips & TricksStarting Boost When Racing Shadow MarioWhen the countdown timer starts as you are racing Shadow Mario, hold forward, then as it hits 2, hold down on Z to crouch, and when the race starts hit A right away and you will turn yellow for a few seconds and get a really good boost that will put you way ahead of Shadow Mario.
Easter EggsBuoy Base Galaxy: Pokemon referenceIn Buoy Base Galaxy, above the tower where you collected the Blue Star Pieces, is a little planetoid that is a sphere with two red panels on top and a lighter bottom with a screw in the middle. It looks exactly like a Pokeball.