Unlock Princess Coins
Once you collect all of the Dragon Coins in the entire game, they will turn into Princess Coins.
Change in Seasons
Ok, this cheat is fairly hard and time consuming. Once you fight your way up into Star World in the sky, you will have to beat all of the levels up there. Soon the mountain in the middle will be acessible, and you can bring mario there. Enter this new realm and you will see a series of new, expert levels. Complete all of these levels to change the season. It will go from the basic Mario, to an orange and brown fall, with new characters, such as the Koopas will turn into Pumpkin Headed freaks. Have fun, and don't forget to save!