World 3-2 (New Super Mario Bros. 2)
From the Super Mario Wiki
World 3-2 is the second normal level in World 3 of New Super Mario Bros. 2. It is an underwater level in a beach area. This level can be accessed by completing World 3-1. There is only one exit, which unlocks World 3-3.
Mario begins in front of a pool of water where there is a small island in the middle of the water being circled by Snake Blocks. A red Warp Pipe takes Mario underwater. A few ? Blocks can first be found occasionally blocked by Snake Blocks above a Whirlpool which will disappear after a short while and then reappear again, like in New Super Mario Bros.. One of the ? Blocks contain a Fire Flower. Then, he will come across more Snake Blocks, Urchins and Cheep Cheeps. After that, another set of Snake Blocks enclosing a Whirlpool with the first Star Coin can be found. This is followed by an ! Pipe. More Snake Blocks and Cheep Cheeps can be found, along with Small Urchins, followed by the checkpoint. Another Fire Flower can be found in a ? Block after that. This is followed by more Cheep Cheeps and Snake Blocks. A P Switch appears on a Warp Pipe on the ceiling, which causes blue coins to appear in an area where Spiny Cheep Cheeps which follows Mario are swimming in. Following that are Snake Blocks where several Urchins are found. Not long after, the blue exit Warp Pipe can be found. Back in the overworld, a hidden block containing a 1-Up Mushroom can be found on a cliff to the left of Mario. Several Snake Blocks can be found circling several floating platforms above water, followed by the flagpole.