World 6-3 (Super Mario Bros.: The Lost Levels)
From the Super Mario Wiki
World 6-3 is the third level of World 6 in Super Mario Bros.: The Lost Levels. The level was originally part of VS. Super Mario Bros. as World 7-3 and was imported into Super Mario Bros.: The Lost Levels.
World 6-3 consists of the player jumping across small bridges while avoiding Cheep Cheeps that are jumping up from below. Koopa Troopas and Koopa Paratroopas are also placed above or on several bridge pieces. The two blocks in the level contain power-ups. Near the end of the level, at the second set of tree platforms, the player will have to bounce off of a Koopa Paratroopa to reach the top of said platforms, which are followed by the Goal Pole.