From the Super Mario Wiki
World 7 is the seventh world in Super Mario Bros. This is the second-to-last world in the game. This world has four different level types: One at ground, one underwater level, one set at seaside, and the final level being a castle as usual. Once again, this world is set during daytime.
||World 7-1 is the first level of world 7, and has quite a few challenges within it. The level features Koopa Troopas, Buzzy Beetles, Bullet Bills, Piranha Plants, and Hammer Bros.; However, this level features no Goombas. This level has significantly more Bill Blasters than the first two levels in World 5. The player must maneuver over large pits and pipes placed randomly around the level. The Hammer Bros. are an additional challenge to the level. A room full of coins can be accessed by entering the first silver Pipe past the first pair of Hammer Bros., this Pipe also having this world's first and only 1-Up Mushroom concealed in an invisible block above the Pipe. Once the player makes it through the level, he or she must move on to the next one as usual. If the player starts the level off as Small Mario, after landing on top of the second Bill Blaster, they should try to hit the leftmost brick block above them in order to cause a Super Mushroom to spawn, which they can get in mid air by jumping off the Bill Blaster and colliding with it as the Mushroom falls of the edge of the above blocks. When trying to get the Super Mushroom concealed inside a single Brick Block placed straight above the Trampoline, the player should go on to the Trampoline after the two nearby Bill Blasters have fired Bullet Bills.
||World 7-2 is once again set underwater. It is also the last level set underwater. This level is identical in set-up as in World 2-2, but with more Bloopers. Similar to World 2-2, this level features Bloopers and Cheep-Cheeps as enemies, and one Piranha Plant appears at the end of the level once the player exits the pipe. The player must maneuver through mazes of bricks and coral as well as avoid the main enemies of the level. If the player is not equipped with the powers of a Fire Flower, then the player must simply avoid all enemies.
||World 7-3 is set at seaside and is the same in set-up as in World 2-3. Some bridges that the player must cross are broken into pieces. As usual, flying Cheep-Cheeps are found in this level; however, unlike World 2-3, Koopa Troopas are also found now. When hitting the ? Block, the player should try to jump up on to the block, as it is very easy to hit by a Cheep-Cheep while standing on the bridge.
||World 7-4 is the last level of World 7, and thus it is a castle level. This level is similar to World 4-4 in the sense that the player must solve the maze in order to confront the False Bowser (whose true form is a Hammer Bro.). Once he is defeated, the player finds the last Mushroom Retainer in the game. That means that Princess Toadstool is in the next (and final) castle. To pass the first maze, the player has to take the bottom path, middle path, then top path. The second maze requires the player to take the top path, middle path, then top path.
Mario swimming in World 7-2.
- Hamma Jamma mentions "World 7-1" as his grandfather's "'hood" in Paper Mario: The Thousand-Year Door, indicating that he grew up as one of the level's four Hammer Bros.
- Worlds 7-2 and 7-3 are duplicates of Worlds 2-2 and 2-3, respectively, except that 7-2 has more Bloopers, and 7-3 has Koopa Troopas in addition to the jumping Cheep-Cheeps. The famous Minus World glitch also leads to an exact replica of World 7-2, but with a different name and without any Flagpoles.