World 2 (Super Mario Bros.)
World 2 is the second world found in Super Mario Bros.. The difficulty for this world is slightly higher from that of World 1. This is the first world to introduce an underwater level, as well as a seaside level.
World 2-1
World 2-1 is a ground level that is similar to that of world 1-1. It is slightly more difficult; It contains more enemies, larger gaps, and more difficult parts of the course to overcome. Small staircases and random Brick Blocks are placed around the level, as well as miniature traps that usually hold one or two enemies in them. The difficulty of this level is still pretty low, but it requires more thinking and more time to get through it.
World 2-2
In this level, Mario, (or Luigi) must swim underwater. During this level, they encounter only two types of enemies: Bloopers, and Cheep-Cheeps (although the Cheep-Cheeps come in red and green). 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.
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 Koopas and 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.
