Book of Sealing
From the Super Mario Wiki
The Book of Sealing was once in the hands of a famous ghost hunter, who single-handedly sealed away several Boos inside. He then set the book to rest on a pedestal in the basement of the mansion. However, at one point, Kamek shows up and opens the book, releasing all of the Boos inside. The ghosts take over the mansion, scaring away the owner.
Outside, the owner is sitting on the front steps of the mansion when Mario and Kersti show up. The owner pins the task of finding and sealing all the Boos once again to them, handing them the Book of Sealing.
Inside the mansion, Mario and Kersti defeat and seal the Boos. In the basement, they discover the pedestal that the book once rested upon. If the book is placed when all the Boos are not captured, then the ground shakes violently and nothing happens; if they are all captured, then the book glows, and Kamek appears again. Using his magic, Kamek breaks the seal a second time; this time, the Boos all form into one Big Boo. After this Boo is defeated, they are all permanently sealed inside the book once again.
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