It's time for the first Ghost House. You can see Big Boo outside, peering through the windows. There are lots of Boos here and the floor and furniture move. There are some moving triple item blocks. Use them to reach the triple item block above for a Fire Flower. Fireballs won't defeat the Boos, but they'll become temporarily transparent, allowing you to walk through them. Go up the stairs and you'll see a portrait of a Boo. Jump into the portrait, which has a Mystery Box behind it. It takes you to a rotating room with ghosts. Wait until the room rotates far enough that you can get the first Green Star. Keep going and you'll see a couch. Stand on it and it will float up to the stamp. At the end of the hallway is a door to the library.
The shelves of the bookcases move when you stand on them. In the lower left corner of the bookcase is the second Green Star. It is hidden behind one of the shelves. Stand on the shelf above it and they will slowly move out of the way. Go up the bookcase shelves to reach the midpoint. There is an invisible block on the back wall so you can reach the item block with another Fire Flower. Go to the right, then go toward the front wall (towards the screen). There are invisible clouds that lead to a 1-up. On solid ground, Big Boo will chase you up the moving steps. Go to the right and pass the pipe, which is fake. Go up the left stairs for a clock. To the right, there is a door near a gap. In the gap are invisible clouds with coins. The door takes you outside.
There are many ghosts out here moving around. The 1-up is fake. Go through the door to go back inside. The floor is moving to the left. There's a clock nearby if you ant to risk it. Keep going to the right and you'll find another couch. It will float to a fake pipe which contains the third Green Star. The door will take you outside again, but the floor is moving to the left. Two Big Boos will chase you, so run quickly. Go past the flagpole, as it is fake. The Big Boos will leave you alone and you'll soon come across the real flagpole.
The stamp is of a Boo.