Captain Toad is a dark cave. Drop down into the mine cart and it starts moving. Look at the GamePad for a first-person view so you can aim your unlimited turnips at things. You can either use the joysticks or tilt the GamePad to look around. Look behind you immediately so you can toss a turnip at the first gem. As the cart moves on the rails, you'll see many POW blocks that will trigger other blocks for coins. There are also many Para-Biddybuds. Past the bridge, on the left, is a large set of brick blocks with a POW Block. Hit the POW Block to destroy the brick blocks, revealing the second gem. You'll go around a corner and see some Para-Biddybuds flying in a circle around a stack of rising and falling blocks with the third gem. Use the POW Block in the stack of blocks to get the gem. After a while, the mine cart will go downhill and stop. Slide down the slide to the Star.
Special Challenge: Defeat all Para-Biddybuds.