New Super Mario Bros. U: Meringue Clouds- Castle -- Ludwig's Clockwork Castle

This castle has lots of platforms moving back and forth on tracks. These platforms can crush you, so be careful. Go past the Spike Beetles and Fire Bro and you'll see a gap with coins in it. Wall jump in the gap for the first Star Coin. Some of the moving platforms are hard to go past, so stand on their tracks, then jump over them. You'll come across a Sumo Bro with the second Star Coin above it. Use the POW Block or freeze the Sumo Bro with an Ice Flower and stand on top of the ice block to get it. Be careful if you use the POW Block because the moving platform below will push it into the void. The midpoint is nearby. Past it is an Amp and some more moving platforms. In between the next two platforms is a Red Coin Ring under a Sumo Bro. Use the alcoves in the ceiling to get past the platforms. You'll soon come to a pit with a giant Dry Bones and donut lifts. The yellow pipe in the ceiling leads to a room with a ? Switch where coins will drop from the ceiling, but not the third Star Coin. Just to the right of the donut lift pit is another platform with Amps and a Sumo Bro. The third Star Coin is on the right side of the platform, towards the center. Drop down the right side and run for the Star Coin when the platform moves to the right, then quickly get out of there, wall jumping if necessary. Just to the right is the boss door. There's an invisible block with a power-up on the right wall.

The cannon will launch you to Ludwig's Airship. Ludwig will fly into the air and split into three of himself. Each of them will make blue fireballs, but only the real one will make three fireballs (the others make 2). They will then drop to the floor, with the real one being the last to drop. Now you can stomp him. To prevent him from flying away, if the real Ludwig is on the right or in the middle, he'll end his shell cycle on the left side and will end the cycle on the right side if he's on the left. Three stomps will defeat him. This opens the path to a spot in front of the tornado surrounding the castle. It's another level with Bowser's Airship.