World 3 (Super Mario Bros.)
World 3 is the third world of Super Mario Bros.. World 3 is the first world in the game to be set at nighttime. This world also introduces the Hammer Bros.. This world consists of two ground levels, one level set at the heights, and one Castle.
 World 3-1
In the first level of world 3, many of the same obstacles are encountered. Among these are Goombas, Koopas, Piranha Plants, gaps, pipes, and of course many Brick Block and ? Blocks. A new addition is encountered however: the Hammer Bros. which come in pairs around two flights of Brick Blocks. The Hammer Bros. throw hammers quite a lot faster than the player can throw fireballs. Upon the steps towards the flagpole are two Koopas. With luck the player can execute an infinite 1-Up trick by jumping on these Koopas. However, as the game uses a signed one-byte integer variable for the player's lives, any number of lives from 129 to 255 will be treated by the game as negative, and will cause a Game Over at the next lost life.
 World 3-2
World 3-2 is yet another ground level that features the basic obstacles yet again. Gaps are slightly larger in this level though, and more Goombas, Koopa Troopas, Koopa Paratroopas and, Piranha Plants.
 World 3-3
World 3-3 is the first of only two levels that are set at great heights at night. This level features Goombas, Koopas and Paratroopas as the only enemies. Due to the lack of enemies, larger gaps are found throughout the level. Moving platforms and suspended platforms are also encountered in this level that require skillful jumping and maneuvering in order to survive.
 World 3-4
World 3-4 is a castle level, so it is the last level. Enemies in this level include firebars, Podoboos, and a False Bowser. The player must jump across pits of lava as well as carefully maneuver through spinning firebars that hurt the player if touched. Once the False Bowser is defeated, the player finds that another Mushroom Retainer is in the castle, and not Princess Toadstool, meaning that Mario still has to continue his journey.