World A

World A is the second secret world that was first featured in the game Super Mario Bros.: The Lost Levels, coming after World 9. The Koopa Troopas from this world on move faster than the normal ones.

World A-1
The player starts off at a place with eight ? Blocks with Koopa Troopas on them, and a Koopa Paratroopa on the ground. If the player jumps in between the gap of the second row of ? Blocks, a power-up will pop out of it. Now the player will see Brick Blocks with three Koopa Troopas walking on them. If the player were to hit the Brick Block on the topmost right, a vine will pop out of it, leading to a Coin Heaven room. The player will see two Warp Pipes with Red Piranha Plants in them. Also, the Brick Block floating high in the air contains a 1-Up.

Now, the player will see many ? Blocks, along with two Hammer Bros. trying to attack the player. One of the ? Blocks contain a Poison Mushroom, while the others contain coins. Now the player will see rows of Brick Blocks with Koopa Troopas walking on them. If the player kicks the Red Koopa Troopa at the top first, and runs along with it so it stays at the screen, he/she shall get a 1-Up. Here is another pipe with a Red Piranha Plant in it, along with a couple more ? Blocks with coins and another Poison Mushroom. Hammer Bros. are also seen in this area, along with more Red Piranha Plants. If the player goes in the one atop the Brick Blocks, he/she will be in a Bonus Room. A Koopa Paratroopa will appear, and the player will see coins along with a pipe and Brick Blocks that are only accessible if the player took the Bonus Room route.

The player will then see two pipes facing each other here, and both of them have Red Piranha Plants in them. Some Koopa Troopas can be seen here, and two Brick Blocks, the bottom one containing a multiple coin block, along with a Trampoline. The player will see Blocks with Koopa Troopas walking on them, along with a platform that will fall if the player is standing on it. The Flagpole can be seen here. Slide down it to gain access to World A-2.

In the SNES remake, an image displaying a Green Koopa Troopa, a Red Koopa Troopa, a Green Koopa Paratroopa, and a Red Koopa Paratroopa is shown before the level starts. However, that image is missing a Hammer Bro., and the Red Koopa Paratroopa never appeared in this level at all.

World A-2
The player will start off from the overworld, and go down a pipe to an underground area. The player will see a trampoline, the Brick Block right over it contains a 1-Up. The player will also see some platforms that will fall down the longer the player stands on them. The player will see a row of Brick Blocks, one of them containing a power-up.

Now a moving platform can be seen, along with pipes on the ground infested with Piranha Plants. A staircase of blocks can be seen. If the player wants to go to the Warp Zone, then it is recommended for the player to break the Brick Blocks and head on toward the lone pipe leading to World B. The player will see a platform that will fall, and then Brick Blocks with pipes infested with Piranha Plants. The player will see a Hammer Bro. here, along with two Bill Blasters. The player will advance, finding a pipe with a lone Piranha Plant, and a pipe leading to the exit. The player will climb up the stack of blocks, slide down the Flagpole, and clear the level. He/She will now have access to World A-3.

World A-3
This level will use clouds as platforms, have strong wind, and will have Flying Cheep-Cheeps as well. The player should keep running while collecting coins. He/She will now see a Blooper, along with some more coins, and then a Koopa Paratroopa that will go horizontally. After that, some more coins and another Koopa Paratroopa going vertically can be seen. A trampoline with the Flagpole, and another vertical flying Koopa Paratroopa can be seen. Slide down the Flagpole to gain access to World A-4. Or, the player can use the trampoline to jump over the Flagpole, and run towards the end. There will be a Warp Pipe leading to World C.

World A-4
The player will start off and see two small firebars and a large one along with a Podoboo that will move faster than usual. The ? Block over here will contain a power-up. The player will see some more lava with two more firebars. A staircase can be seen here, and at the ledge right after it, a Koopa Troopa will walk by the player. The player will see small stone blocks going down the lava, splitting it into sections in which Podoboos are jumping about. The player will cautiously advance forward, and then find a Bill Blaster hanging from the wall. The player will see yet another Bill Blaster, this time on the ground.

The False Bowser will start shooting fireballs at the player now. The player will then see one final Bill Blaster, with a bed of lava for him/her to cross. Then a small staircase leading to the fight with False Bowser will appear. False Bowser will attack by throwing hammers. This time, the False Bowser is actually a Red Koopa Troopa, and will fall into the lava once the player defeats it. The player will rescue 5 Mushroom Retainers, but the princess isn't in this castle. The player will now have access to World B-1.