World 3-Fortress 2

 2 is the ninth overall and second fortress level of Water Land in Super Mario Bros. 3. This level can be played after completing World 3-7, and beating this level unlocks the next level.

Layout
This level spawns Mario on a platform next to water and a Warp Pipe at the bottom of the water. This Warp Pipe leads Mario to another, submerged area. Mario must swim past a Roto-disc and a two Cheep Cheeps. A ? Block lies between the two Cheep Cheeps, and it holds either a Super Mushroom or a Fire Flower. This ? Block is the only source of power-ups throughout the entire level. Past the ? Block and the second Cheep Cheep is another Roto-disc and a new Warp Pipe. Between the Roto-disc and the Warp Pipe is another Cheep Cheep, which forces Mario to swim as high or as low to the ground as possible in order to successfully dodge the Roto-disc and Cheep Cheep. The Warp Pipe leads Mario to the third area of the fortress: another underwater setting. Mario encounters two Stretches, marking the enemy's first appearance in the Mario franchise. He must swim above, below, or in between the two Stretches to another series of Stretches. This area contains three more Stretches. Past these enemies is the final Warp Pipe which takes Mario to Boom Boom.

Enemies

 * Roto-discs
 * Cheep Cheeps
 * Stretches
 * Boom Boom (boss)

Level Statistics

 * Power-ups: 1 (Super Mushroom or Fire Flower)
 * 1-Up Mushrooms: 0
 * Secret areas: 0