Super Mario Galaxy Tips

Last Suprise
After you complete the 'Grand Finale Galaxy' (obtained when 120 Power Stars are retrieved by Mario and Luigi), talk to the Mailtoad near the Power Star (121st star). He will ask you if you want an exclusive letter. Select 'yes' and grab the star. Later, go to your Wii-mailbox and you will see that a letter from the Super Mario Galaxy staff is inside.

Spoiler: Read for Spoilers!
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Click on the little photo in the upper-right hand corner and you will see a picture of Mario/Luigi (depending on which character you completed the galaxy with). I am not going to tell what the pictures are, so you might as well find out on your own!