Big Boo Battle

In Super Mario 64 DS, after Mario was unlocked, with 15 stars obtained you can access Big Boo's Haunt by defeating the biggest boo in the back of the castle, then it drops a cage. Go to the second floor,use a power flower or wall kick and enter the Luigi painting and hear King Boo laugh hear which door he's laughing from and go, if you enter a wrong door or fall off, you'll start from the beginning without losing a life. There's 2 stars in this level one, you need Wario to break the black brick where the 8th and last red coin is and get a star, another Luigi can use the power flower and go through the wall getting the star. Once you reach the last door you'll fall into a hole and you'll see a mirror with Lakitu in it and disguise as Luigi and King Boo will talk Mario. Upon defeating him, Luigi is unlocked!