Captain Toad finds himself in a room with the Star in the center. Approach the Star and a tower rises up under it. Purple water starts rising. Run to the left, where platforms will drop into the water so you can get out of the water. Follow the path and you'll encounter Boos. Do your best to dodge them, as you don't have enough time to defeat them with your headlamp. They'll disappear after you go around a couple of corners. You'll find the first gem on a seesaw. While you run, it will tip up enough for you to reach it. Go past the second gem, which you can't reach. Cross the seesaw around the corner, then double back. Platforms will appear behind you that allow you to reach the second gem. Walk up the ramp and you'll see a partial ring of Peepas. You may have time to defeat them. Let a few platforms fall so you can go past them without taking damage. Go around the corner and use the seesaw to get the third gem. Turn the corner and a giant Boo will appear behind you and a Boo will appear in front of you. Dodge or defeat them, then go around the corner, where you'll find more Boos and Giant Boos. Defeat them, then proceed on the flat platforms. At the end, you'll find a hidden Gold Mushroom. Run up the ramp to the Star. The Boos, platforms, and purple water will disappear when you step on the platform.
Special Challenge: Find the hidden Gold Mushroom.