CheatCodes.com: Unlockables for Super Mario Galaxy for Wii

Luigi
Finish the whole game (Which means to get all 120 stars), then go back to the Comet Observatory and talk to Rosalina and ask to fight Bowser one more time. Once you defeat Bowser, Luigi will become available.
Submitted by: [Firenze] Added: 21 Nov 2007	Report this Unlockable as Broken

121st Star
There's actually 121 Stars in the game, not 120. To get it, you must first have all 120 Stars. This unlocks Luigi. Beat the entire game with Luigi, defeating Bowser at the end. After this, a new galaxy will be unlocked. Finish this final galaxy to get the 121st Star.
Submitted by: deason82 Added: 07 Feb 2008	Report this Unlockable as Broken

Death Count
The Grand Finale Galaxy, which is the secret galaxy that can be unlocked after 120 Stars are gathered with both Mario and Luigi, holds another secret. Once the final Star is acquired with both characters in this galaxy, you will be able to see your death count on your save file. This will allow you to see how many times you died while playing the game with both Mario and Luigi.
Submitted by: deason82 Added: 07 Feb 2008	Report this Unlockable as Broken

Super Mario Galaxy for Wii Unlockables