Ludwig's Clockwork Castle
From the Super Mario Wiki
Ludwig's Clockwork Castle, or Meringue Clouds-Castle, is the Castle course of Meringue Clouds in New Super Mario Bros. U. It is not only the last main course in Meringue Clouds, but the last Koopaling castle in the game. It is unlocked via completion of Snaking above Mist Valley or via the secret exit of Spinning Spirit House and its own completion unlocks Boarding the Airship.
The castle's main obstacles are moving platforms operated by gears. There are many instances where the platforms can crush the player if unaware. The most prominent enemies are Bony Beetles, Sledge Bros., and Amps, although there are less enemies than usual.
Ludwig von Koopa is the boss of the castle, with his boss arena taking place on the crow's nest, like Roy's boss arena. In battle he levitates in the air while making two duplicates of himself, and all three will blast fireballs at Mario before dropping onto the ground. If the duplicate is jumped on, it will simply disappear. Fireballs do not affect them. One way to find out which Ludwig is the real one is to see which one lands last, and then jump on that one. Also, the duplicates only fire two fireballs at a time each, while Ludwig will fire three. When the fight starts off, after shooting their fireballs, they disappear before landing. After the first stomp, the duplicates don't disappear, making it a little harder on which is the real Ludwig. After the second stomp, not only do Ludwig and his duplicates shoot faster, but swap positions, but the real Ludwig still shoot three fireballs.
Additionally, during the boss battle, the tornado and a silhouette of Peach's Castle and Bowser's airship flying around it can be seen.
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