Toadette finds herself in a large mansion. It's pretty dark here, so keep your headlamp on. Look behind you into the dark corner to find Blue Toad, who will give you a 1-up Mushroom. Once you drop down to the floor below, Boos will appear. There are some holes in the wall on the dark side of the mansion. Go through the left one and you'll find a ladder. Climb up it and walk to the left along a narrow path to the first gem. Once you get it, Peepas will appear and circle around you. Walk back towards the ladder, but drop down away from the wall a short distance. Walk towards the nearby ladder to the third floor and you'll find the second gem in an alcove. Go to the first floor so you can return to the second floor, then climb the ladder to the third floor. There's a gear at the top you can spin. Rotate the gear so that the third gem is on the opposite wall to you. Carefully walk across the narrow path to the third gem. When you get near where the paths cross, Big Boos will appear. Stay where you are and shine your light on them to defeat them. Walk to where the paths cross, then go left, then towards the Star. Drop down and avoid the Boos to get it.
Special Challenge: Collect the 1-up Mushroom.