Super Mario Galaxy Easter eggs

Princess Peach's letter
Mailtoad will receive a letter from Princess Peach whenever you save the game with at least 10 lives. You will get 5 1-UPs from the letter if you're playing as Mario and 20 1-UPs if you're playing as Luigi. You will also receive her letter if you lose too many lives on a galaxy. In that case, you will receive 5 1-UPs regarldess of who you're playing with.