World 7-4 (Super Mario Bros. 3)
From the Super Mario Wiki
The player starts next to some Warp Pipes, which lead to the underwater section of the level. Before entering the pipe and if the player is powered-up with a flight item, the player can fly over the large structure to the right and find two 1-Up Mushrooms.
Entering the Warp Pipes will take the player to an autoscrolling underwater location and several Spiny Cheep-Cheeps will move through the barriers throughout the start of the level and Lava Lotuses placed on the ground. Shortly after the first ? Block, Big Berthas and Scattering Bloobers will start appearing, with Big Berthas usually placed in confined areas and Scattering Bloobers usually in open ones. Around the point when the first Scattering Bloober shows, the stage will start scrolling up then resume moving horizontally through a group of Jelectros that slightly bob up and down, with another Big Bertha and two Scattering Bloober at the end of the group. Spiny Cheep-Cheeps will resume appearing throughout the rest of the level and player will encounter another Big Bertha and one final Lava Lotus before the pipe leading to the goal.