From the Super Mario Wiki
Pipeline Lagoon, otherwise known as World 3-5, is the fifth course of World 3 in Super Mario 3D World. This level is the first one in the game to take place underwater. It is unlocked via completion of Magikoopa Blockade, and its own completion unlocks Mount Must Dash and Switchboard Falls.
Pipeline Lagoon additionally appears in the background in Super Mario Maker 2, in the underwater theme of the Super Mario 3D World style.
Pipeline Lagoon starts on a small beach with some Goombas relaxing in the water. Across the water is a green Warp Pipe that takes the player to the next portion of the level. Here, the bodies of water are deep enough for characters to go underwater. This area contains some Cheep Cheeps and Porcupuffers. When the player transitions through the Clear Pipe to the next area, there is a massive shipwreck in the background. A Checkpoint Flag appears soon after, followed by an area where Porcupuffers appear through holes in the wall in a set pattern. A nearby pipe leads the player to the Goal Pole.
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