World 1 (Super Mario Bros.: The Lost Levels)
World 1 is the first world found in the Japanese version of Super Mario Bros. 2. The world is well-known for bearing many similarities to the original game's, but the sprites had been advanced and the levels were much harder. This was the first world in any game to introduce the Poison Mushroom.
World 1-1
The player starts out next to the castle on a rocky pathway. As the player moves forward, he will encounter a jumping Koopa Paratroopa. The player must avoid this enemy, and then the player will be standing under a layer of bricks. If the player hits the brick that's second-to-the-left, a mushroom will appear. Then the player must avoid the two piranha plants and jump over a green pipe. Over the tree next to the pipe there is an invisible 1-Up block that the player can get (optional).
After jumping over a hole, the player will come across a swarm of Koopa Troopas. The player avoided these and jumped over another two pipes (one of which contained a piranha plant, and the other lead to a coin room). In the last ? block of the level, the player found a Super Mushroom/Fire Flower (optional).
Lastly, the player reached the Ending Staircase of the level, and the Flagpole afterward.
World 1-2
This is the first underground level of the game. There is a small cutscene at the beginning of the level showing Mario or Luigi (whomever the player is playing as) walking into a pipe in the overworld. The plumber will then plummet into the underground.
In this level, there are goombas, piranha plants, and koopa troopas to avoid, and a large canyon where the player must quickly jump over mushroom floors (which drop if stepped on) to cross. As it is the first underground level of the game, it is also the first time the player can go to a Warp Zone, which leads to World 2-1.
World 1-3
World 1-3 takes place in the heights, or mushrooms in the overworld. The player must jump over large gaps to get from mushroom to mushroom. There are also many enemies to avoid, most notably overworld bloopers (this is the first appearance in any game of a blooper above water). The player must also cross the perilous mushroom platforms, which drop on contact. There is no staircase in this level, the player must jump on a mushroom to get to the flag. Clearing this level gives the player access to the world's castle.
World 1-4
World 1-4 is the first castle level in the game. It is very short, and the player needs only to jump over nine holes while avoiding the nine firebars, and then the player will reach the first False Bowser in the game. If the player is Fire Mario/Luigi, (s)he could hit the false Bowser five times in order to reveal a goomba operating the costume, and then the false Bowser would be defeated. Another option to defeat the false Bowser was to jump over it and hit the golden hammer behind it.
After defeating the false Bowser, Mario/Luigi will walk up to a Mushroom Retainer, who will say "Thank You Mario! But Our Princess Is In Another Castle!"
