World Mushroom-2 (New Super Mario Bros. 2)
From the Super Mario Wiki
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It begins with Mario in front of a pool of water infested with Urchins, an orange platform and a pipe leading underwater. First, two Urchins can be seen next to a wall which moves after a set amount of time passes. Two ? Blocks follow, one of them containing a Fire Flower. Urchins then begin to bounce and roll down on slopes on the floor. Several walls will then move down halfway, covering several coins. A Deep Cheep appears, followed by more Urchins. Several more Deep Cheeps and Urchins will then appear, followed by the checkpoint. A Roulette Block can then be found, followed by two Urchins and a Red Ring. More Urchins fall and the floor moves up slightly at certain spots. More Urchins and Deep Cheeps appear. Parts of the floor and ceiling can be found enclosing Urchins which will come out when the floor or ceiling opens up. After that area, Mario needs to navigate through an area full of Urchins. At the end is the exit pipe out of the water. Several blocks in the area can help Mario reach the top of the flagpole, which is a short distance away.