Roy's Conveyor Castle

Roy's Conveyor Castle, or  is the castle of Rock-Candy Mines in New Super Mario Bros. U. This castle contains iron blocks that float on lava and Dry Bones. It is unlocked when Shifting-Floor Cave is completed and its own completion opens the path to Meringue Clouds and Land of the Flying Blocks. Additionally, the course can be entered via a Exclamation Mark Switch bridge to the backdoor of the castle. The boss of this stage is Roy Koopa.

Level Overview
The player will first ride an iron block across some hot lava and encounter a Dry Bones and a Bony Beetle. After that, he or she will pass by another Bony Beetle and ride on some more iron blocks in order to avoid the lava. On the way, the player may collect some coins. After that, the player will reach an area where he or she must hit a switch, thus causing a bunch of blocks to fall on top of the surface of the lava. The player can then get on top of them and make his or her way to the door. The player will then enter the door, launch themselves out of the cannon, and proceed to fight Roy Koopa.

Star Coins

 * Star Coin 1: In order to get the first Star Coin, the player must allow the first iron block to fall on the surface og the lava and quickly dash towards the Star Coin.
 * Star Coin 2: While floating on an iron block in the middle of the level, the player must wall jump to a hidden Warp Pipe which leads to a hidden room. After entering the hidden room, the player must act quickly by dashing to the second Star Coin and back before an iron block falls.
 * Star Coin 3: Access to the third Star Coin requires the secret entrance into the back of this castle on the world map. Next, Mario must step on a switch in order to cause a bunch of iron blocks to fall overhead. After that, Mario can now walk on top of the iron blocks and get the third Star Coin before the last iron block falls and block the path to the Star Coin.

Second Entrance
The second entrance is automatically unlocked upon completion of Screwtop Tower. However, it will not be accessible under normal circumstances as all paths to the second entrance requires the use of the red Stretch Blocks to the right of Screwtop Tower, which is impossible to have been stretched when Mario is at Screwtop Tower because the south path leads to a blue switch which would have been automatically stepped on and the west path leads to blue Stretch Blocks which must have been used to cross the abyss, and there are no red switches nearby. To get to the second entrance, the player must do one of the following (in addition to completing Screwtop Tower):
 * 1) Complete Waddlewing's Nest and Thrilling Spine Coaster (which requires locating the secret exit in Grinding-Stone Tower). The player can then step on the red switch to the east of Waddlewing's Nest and use the secret path through Thrilling Spine Coaster to reach the now stretched-out red Stretch Blocks and the second entrance. or
 * 2) Find the secret exit in Walking Piranha Plants!. This unlocks a path to a red switch and bypasses the blue switch between Walking Piranha Plants! and Screwtop Tower. or
 * 3) Complete this level once normally. A path to the second entrance will then be opened allowing the player  to get the third and last Star Coin.

Enemies

 * Dry Bones
 * Bony Beetle
 * Bullet Bill (during the boss battle)
 * Missile Bill (during the boss battle)