New Super Luigi U: Meringue Clouds- Ghost House -- Vanishing Ghost House

In this Ghost House, the floor slowly disappears, piece by piece. There are fake item blocks here. The first Star Coin is over some real item blocks. Keep going and you'll come to a rotating floor. Transfer to another rotating floor, which will drop down. You'll find the second Star Coin over a real item block to the right. Keep going and you'll find a door. Drop down underneath the door from the left and you'll find the third Star Coin behind the hidden stairs. Go up the stairs, then walk through the wall to find a hidden door. This will take you to the flagpole.