Get access to the basement (fight the first Bowser) and get 15 stars or 50 (some high number) so that the yellow rabbit appears in the basement. Chase after him and grab him. Now, when he gives up, pick him up and bring him to the door you used to enter that area. Walk into the right side of the door and press Z so you start to crawl and drop the bunny. Still in crawling mode, turn around so you're facing the bunny and then stand up. Pick him up, turn around, and drop him on the other side of the door. Now, back up so you get pushed back to the room you were in and walk through the door. There's the rabbit, outside of his normal area! You can do this to many doors and bring the rabbit around the castle. You can also use him to access areas you wouldn't normally be able to (see Beat the game with just 16 stars).
Submitted by: Dom Dunc