World 2 (Super Mario Bros.)
World 2 is the second world found in Super Mario Bros. The difficulty for this world is slightly higher than that of World 1. This is the first world to introduce an underwater level, as well as a seaside level.
 Level Information
 World 2-1
This level happens in a grass area, such as World 1-1. Mario starts near three Brick Blocks, two empty and one containing a Super Mushroom. Mario will then pass through a five-tile tall half-pyramid with a Goomba. On the other side, there will be some Brick Blocks and two green Koopa Troopas walking under them. There's also a hidden Block that allows Mario to gain a 1-Up Mushroom. Ahead, the plumber will meet two Goombas and a Piranha Plant in a pipe. After it, ten Question Blocks and a green Koopa Troopa walking over the bottom line. Mario will, then, find some more Brick Blocks and a Pipe. There will also be some Question Blocks and, above them, some Brick Blocks. One of them contains a Beanstalk, that will lead Mario to a Coin Heaven. Ahead, Mario will find some pits and pipes with Piranha Plants. There will be a green Koopa Troopa walking near a pit and some green Koopa Paratroopas and a Piranha Plant in a pipe. After it, a trampoline, that will help Mario to reach the top of a ten-tile block tower that allows Mario to touch the highest point of the Flagpole, that is straight ahead.
 World 2-2
In this level, Mario (or Luigi) must swim underwater. During this level, they encounter only two types of enemies: Bloopers, Cheep-Cheeps, which come in red and green (Red and Grey in the NES and Game Boy Color version), and one Piranha Plant in the final pipe of the level. The brothers' only defense in this level are fireballs; If the player can not throw fireballs, then the player must simply avoid all enemies. Though this level is underwater, gaps are still found here. The end of the level features a pipe that takes the player to ground level, where Mario or Luigi can jump on the flagpole. If a player is killed by a Blooper in this level then there will be no more Bloopers when the player starts again.
 World 2-3
This level is a sea-side themed level, though the sea can't be seen. Through most of the level, the player must walk across bridges (broken and whole) while avoiding jumping Cheep-Cheeps as well as gaps. The level is relatively short, but requires tedious concentration to make it through it alive.
 World 2-4
This is the last level of World 2, thus it is a castle level. The player must jump over several gaps of lava as well as many rotating firebars. Podoboos are first seen here; They are basically fireballs that jump from lava pits, making jumps even more tricky for the player. Once the player reaches the end of the level, he or she must defeat the False Bowser to continue. They find that a Mushroom Retainer is there and not Princess Toadstool, meaning that the journey must go on.
 Enemies Introduced