Super Mario Galaxy Cheats :
DuCk in thin air!
When you are Luigi, go to the level: The Fate Of The Universe. Then, when you get past the part where Bowser Jr. comes up with Princess Peach Peach, DO NOT GO TO BOWSER! Instead, go to the place where the circle part ends. Then, run to the edge and JUMP off the edge before Luigi falls! BUT KEPP HOLDING A! Once you start falling, an invisible platform will be there, and you will be ducking in thin air! But the bad part is, after a second or two, you will fall and die.