|Location(s)||Big Boo's Haunt|
|Received When Killed||Yellow Coins/Red Coins/Blue Coins|
Boos are small, spherical, and completely white. They have a blue mouth, which is changed to red in the DS version. Their mouths contain four sharp teeth, with the outer ones being longer. Their eyes are blue in the N64 version, while they are black in the DS remake. They also have two flaps that serve as "hands" on their sides, although they don’t use them. If the player looks directly at a Boo, it will turn transparent, revealing a blue coin inside their body.
In the Super Mario 64 series
After collecting a single star, a regular-sized Boo will appear in the middle hallway of the castle, and large number of Boos can be found in the rear courtyard. Eight of these Boos contain Red Coins in the DS remake. Once the player collects 12 stars (or 15 in the remake), a larger Boo will appear in the hallway. If the player ventures to the courtyard, they will spot a a larger Boo, which can be defeated to get to Big Boo's Haunt.
In the DS versions, Boos move a bit faster, but they are still slower than Mario and even Luigi. However, they are faster than Yoshi and Wario. Furthermore, Yoshi can't defeat Boos; eating them causes Yoshi to spit them out, and any attacks he can perform do not harm Boos. Because of this, Big Boo's Haunt is the only main course that Yoshi cannot enter.
- Courtyard in Peach's Castle
- Big Boo's Haunt
- Big Boo Battle (DS only)
Boos have no attack other than trying to rapidly fly into the player. When the player is attacked, they lose two bars of health. If the player is attacked by a larger Boo, they will lose three bars of health.
In a similar fashion to the earlier Mario games, Boos will turn mostly invisible if Mario faces them. If Mario faces a different direction, they will reappear and try to attack. To defeat a Boo, Mario must jump over the Boo and Ground Pound it.