Lemmy's Swingback Castle
From the Super Mario Wiki
Lemmy's Swingback Castle, or Acorn Plains-Castle is the castle level of Acorn Plains and the first Castle of New Super Mario Bros. U. The course contains lava and rocking platforms suspended by chains. It is the final course of the Flying Squirrel Pack. It is unlocked by completion of Mushroom Heights or Rise of the Piranha Plants, and its completion unlocks Layer-Cake Desert and its first level, Stone-Eye Zone.
Suspended over lava, players must use the blue rocking platforms to navigate and maneuver over the lava. Later in the course, there is a sub-level that contains a Star Coin with a platform almost entirely covered in lava. At the end of the castle, there's a blue door which leads to the top of the castle. The player must then use the red and black cannon to shoot themselves into Lemmy Koopa's airship. This level features a Super Acorn item, and as in most Castle and Tower levels, there is a hidden Fire Flower towards the Boss Door.
The boss of the course is Lemmy Koopa, who now uses bombs (with the same star pattern as his bouncing balls) and tosses them at the player while periodically rolling around the arena. After getting hit two times, he starts throwing larger bombs that have bigger blast radius.
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