Mario begins the level near some Brick Blocks between stone blocks, with a Buzzy Beetle and a Koopa Paratroopa on top of them. Mario can find a Super Mushroom or a Fire Flower in the very first Brick Block of the stage. Furthermore, Mario encounters another row of Brick Blocks, with a Koopa Troopa on top of them, and three Goombas walking in Mario's direction. Mario must follow a straight path with three Koopa Troopas and a Hammer Brother at the end, until he reaches a pipe. To reach this tall pipe, which contains a red Piranha Plant, Mario must find an invisible Question Block and jump on it. In the other side of the pipe, Mario finds a Bill Blaster in the ground, and an abyss ahead of it. Mario eventually finds two pipes, with red Piranha Plants, and a Hammer Brother near a row of Brick Blocks. After this, Mario encounters two Koopa Paratroopas, and a row of ? Blocks, all of them containing coins, except for the last one, which contains a Poison Mushroom instead. When Mario reaches a small stair-like structure, the wind starts to blow Mario, who must use several platforms to cross a large pit with water that Mario cannot swim in. There is a pipe to the left, in the corner, which Mario can enter if he uses the first platform. Upon entering it, Mario is taken to an underwater section, where he must swim, while collecting coins and dodging Bloopers, a Koopa Troopa and a Koopa Paratroopa. Once Mario enters the pipe in the end of this section, he is taken to an area where he must jump in several pipes containing red Piranha Plants, until he reaches the flagpole. Mario must slide it down to end the level.
When the level begins, Mario enters a pipe which takes him to the underwater. In this level, Mario must swim across a large underwater area, while dealing with Cheep Cheeps and Bloopers. Mario finds the first enemies of the stage near some corals, which block the hero's path. Mario must swim between these corals in order to advance, but this is dangerous, as Mario is forced to swim near an abyss. Mario needs to dodge several Cheep Cheeps and Bloopers, until he finds some platforms going from the top to the bottom of the screen. These platforms can push Mario to the nearby pit, thus forcing the hero to quickly swim between them. Once Mario crosses these dangerous platforms, Mario finds a lone Koopa Paratroopa and a Koopa Troopa, which cannot be stomped underwater. Mario eventually finds the pipe leading Mario to the flagpole. Mario must slide it down to complete the level.
This level takes place in a long bridge, where several Cheep Cheeps jump and try to stop Mario's progress. In the beginning, Mario is greeted by jumping Cheep Cheeps, Koopa Troopas and Koopa Paratroopas. After this, Mario finds narrow pieces of bridge in the air, above a pit. He must carefully jump on these bridges and make it to the next bridge. A Question Block can be found here, but the only way to collect its item is by stomping a Koopa Paratroopa, which can be very dangerous. Once Mario reaches the next bridge, he must run through it, while dodging Cheep Cheeps, Koopa Troopas and Koopa Paratroopas. Mario eventually finds two solid platforms, and a Question Block which contains a power-up. After making his way through another section of small bridges, Mario finds a Koopa Paratroopa, which, when stomped, gives Mario boost to reach some tall platforms. Once Mario crosses these platforms, he finds the flagpole near a Koopa Paratroopa. Mario has to slide it down to beat the level.
This is a castle level, and as such, the last level of the World 6. Mario begins near a wide pool of lava, where he must utilize a small platform to reach solid ground. There is a pipe with a red Piranha Plant, and a Fire Bar ahead of here. Mario must overcome a path puzzle in which, he must chose the right path, otherwise the level repeats and he is forced to chose another path. In this case, Mario must cross the bottom path, until he reaches a long, upside-down pipe with a Piranha Plant in it. After this, Mario finds a Hammer Brother and three paths near a pool of lava. Mario must chose the upper path, which leads him to some pipes with Piranha Plants in it. Mario needs to walk along these pipes, eventually finding a lava pool and a Fire Bar in some blocks. Mario has to jump on these blocks until he finds some platforms going from the top to the bottom of the screen. Mario encounters three paths in this area, and he must cross the bottom path, where he finds a Lava Bubble and some Fire Bars. Then, Mario must use a small platform above the lava to reach the Bowser Impostor's chamber, while avoiding the fireballs shot by the Bowser Impostor. Once Mario reaches the chamber, he can either defeat the clone with fireballs, revealing a Blooper, or touch the axe to destroy the bridge, sending the impostor to the lava. Either way, he ends up rescuing the Toad, thus completing World 6.