We need 200 Star Coins to unlock this level. It's an automatic sidescroller with the red and blue flipping platforms. The first Star Coin is on the second Airship, to the right of the green pipe. The green pipe leads to a room with Boom Boom, but you don't need to battle him. We roll through the bricks in the wall to continue. At the back is the second Star Coin over the red part of a flipping platform. There are more flipping platforms after that, with the third Star Coin over it. At the end of that is the flagpole.