Super Mario 64/Big Boo's Haunt

Big Boo's Haunt is Course 4 of Super Mario 64 DS. 15 stars are required to access it. Enter one of the wooden doors on the left or right side of the staircase on the first floor, then follow the Boo down the hallway and into the courtyard. After that, go to the far left corner and defeat the large Boo there, then walk into the cage to enter Big Boo's Haunt.

Star 1: Go On a Ghost Hunt
In this level, enter the building in front of you. Next, enter the second door on the right, and defeat the two Boos in the room. After that, leave the room and enter the leftmost room on the rear wall and defeat the Boo in there. Then, go in the other door on the rear wall, defeat the Boo in there, move on to the next room and defeat the Boo in that room, then go back to the large main room. It takes three hits to best the big Boo, after which the staircase will rise and lead to the first star in this level.