World 3-A (New Super Mario Bros. 2)
From the Super Mario Wiki
This is an underwater level. Mario begins on an orange platform in front of a pool of water where there is a strong water current and Cheep Cheeps. A ? Block containing a Fire Flower can be found, followed by the Warp Pipe going underwater. When Mario first enters the water, the player can see strong water currents coming from yellow pipes on the left side of the screen. Mario will immediately move with the current. A P Switch can be found on the ground just to the right of the pipe, which will make blue coins appear. Cheep Cheeps and Big Cheep Cheeps are the enemies Mario has to avoid. After that, there will be a fork in the path, where he could change paths through a hole if he took the wrong one. After the fork, Mario will then reach a red pipe which takes him to the next room, where there are no currents. Inside, there are Cheep Cheeps moving in circles. Going forward there are currents in a small maze with mini Urchins. After that is the checkpoint. A red pipe will then warp Mario to another area with current. Here, Mario needs to avoid the Urchins and mini Urchins. There is also a Roulette Block where the current changes direction. The player has to navigate through the area while avoiding the Urchins to reach the exit pipe. Back in the overworld, Mario will then cross calm waters using the orange platforms. This is followed by the flagpole.