World 3-Castle (New Super Mario Bros. 2)

 is the final castle of World 3 in New Super Mario Bros. 2, either the first half. It is a water-themed castle cramped with dangerous Grinders that attempt to hinder Mario. The boss of this level is Wendy O. Koopa.

Layout
Mario begins on a platform which is being circled by a Grinder. This is followed by two ? Blocks, one of them with a Super Leaf. This is followed by more Grinders bouncing from their tracks. A Bone Goomba follows. This is followed by more Grinders and a section where Mario has to go trough a pipe. From this point, the whole level is underwater and auto-scrolls. Another ? Block containing a Super Leaf can be found. The next section features many Grinders and large Grinders on tracks along the path. Another Super Leaf can then be found. A Bone Goomba can be found, followed by more large Grinders in an area with platforms that move up and down. The player then goes trough a pipe. There's a section where jumping Cheep Cheeps are found. As the player goes underwater again, they will meet Urchins and Circling Boo Buddies, followed by Sushis and Cheep Chomps. This is followed by the boss door.

The boss here is Wendy O. Koopa, whose battle takes place on a long orange platform with water below. Her attacks are mainly water-based. She can cause the room to be filled with water in which state Mario cannot attack her, except with fireballs. Blowing her whistle causes Cheep-Cheeps to swim in the water, or cause them to jump out of the water below when it is dry. To defeat her, Mario has to stomp on Wendy's head three times when it is dry, or use Fire Mario to attack her at any time.

Star Coins

 * Star Coin 1: The first Star Coin can be found enclosed by a Grinder in the section where Mario climbs up orange platforms. One way to obtain it is to activate a hidden block with a 1-Up Mushroom below the Star Coin by hitting it from a small orange platform, then jumping up from there. Otherwise, Mario should wait till the Grinders are not obstructing him and then jumping to the Star Coin.
 * Star Coin 2: The second Star Coin can be found after the checkpoint right after the section with giant Grinders, being guarded by a single Dry Bones on a platform with Grinders coming from the water.
 * Star Coin 3: At the boss door, look for a hidden block on the right wall. Climb up that block to reach a ledge leading to the Star Coin.