The first star of Big Boo’s Haunt will have you hunting down some ghosts inside of the mansion. The main entrance will be right in front of you whenever you begin the level, so head through the doors to see another five doors on the first floor. The first door on the left does not have any Boos, so you can completely ignore it for now. With that said, the other four doors on the first floor will contain the Boos you need to defeat in order to get this star. So, head through the second door on the left side to find yourself in a room with some bookshelves, a table and two chairs.
Be aware that the chairs in this room will come alive and attack you. There will also be a painting of a Boo covering its face on the wall, which will be the key. When the coast is clear, turn your back to this picture and two Boos should come through that painting. A good Ground Pound when you’re not looking at them will take care of them. Upon defeating a Boo, there will be a text box that appears goading you. Anyway, return to the main lobby and enter the next door to the right, where you will see a Mr. I and another Boo.
The next room will be the right one, in the back, in the main lobby. Cross the bridge, making sure you don’t fall, and defeat the Boo on the other side. If you should fall, you have to go all the way around, to the elevator, bringing you to the shack you can see from the beginning of the level. Once you get that fourth Boo, go through the door near it to a room with some thin ledges. The last Boo you will need is in this room. Defeating all five will get a different text box to appear, so return to the main lobby to find a Big Boo waiting for you. Treat this one no different than the others, except it takes three hits to bring it down. The star will go to the second floor, so approach the different-colored floor to make stairs appear.