Big Boo Battle

Big Boo Battle is a level exclusive to the Super Mario 64 DS. Upon completing it, Mario will earn the key to unlock Luigi. The boss that Mario fights here appears to be King Boo, though he claims to be named Big Boo.

This level is actually a pocket level of Big Boo's Haunt, which is where the entrance is located. It is the only one of the three levels required to save the playable characters to be entered inside of another level, and the entrance can be found in the Luigi Painting on the third floor of the mansion. Being a pocket level of Big Boo's Haunt, Big Boo Battle takes on a haunted house setting. It is a maze, and the goal is to find the correct path, as taking an incorrect door (or falling) warps Mario back to the start. The player can determine the correct path by listening to King Boo's laughter and determining the direction it is coming from.

The first room of the level is a room with a spinning floor and four doors. The second room is a room with four bridges connected to a central platform, which collapse if the player attempts to walk across them, and four more doors. The third room has four platforms near four doors and a central platform, and the fourth room has several platforms near the four doors, as well as several moving platforms. Entering the correct door for each room leads Mario to a room with a collapsing bridge with a section with several moving platforms and a Boo portrait on the other side. The entrance to the Big Boo battle itself is on the upper segment, down the hole on the other side of the platform. Defeating King Boo earns the player the key to unlock Luigi. It is the only one of the two secret levels in the game to be inside a main level; the other being Behind the Waterfall in Hazy Maze Cave.

Star 1
Find the eight Red Coins that are spread out throughout the level. This Power Star requires Wario in order to obtain it, as his strength is needed to break a black Brick Block containing a Red Coin. There will be two stars if all but the first red coin is collected, then if the player goes back to room one, they will hear the star intro sound, but see the wall. Navigate the maze again, two stars are there. The second star does not count towards the star total.

Star 2
There is a hidden Star behind the Boo portrait in the last room before the boss. It requires Luigi's Power Flower ability in order to reach it.