It's raining in the canyon, which is filled with purple water. Drop onto the raft, which has unlimited turnips. The raft will start floating along and the Hammer Bros will start attacking. Toss the turnips at them. Hit the POW Block to get rid of the third Hammer Bro, then exit when you reach where the POW Block was. The tunnel leads to the first gem. Drop down from there and pull the handle to reach another tunnel. Inside, you'll find a wall of brick blocks with some POW Blocks. Touch the POW Blocks on the GamePad to break through the wall. Pull the handle to make the platform rise. There are some moving plants here. One has the second gem. The other has a pickax. Break the bricks to find many plants with multiple coins. Go back towards the second handle and you'll find another raft with unlimited turnips. Drop onto it and use the turnips to defeat the homing Bullet Bills and the POW Block and the third gem. At the end of the raft ride, climb the ladder and pull the handle. Go under that area to the other side and you'll find a hidden Gold Mushroom. Walk up the stairs to the Star.
Special Challenge: Don't take any damage.