World 1-4 (Super Mario Bros. 3)
From the Super Mario Wiki
This is an autoscrolling athletic level, featuring moving platforms that fall down as soon as the player lands on them. If Mario or Luigi stay too long next to a moving platform or a Brick Block, the autoscrolling level will squish them, instantly killing them and causing them to lose a life.
The player must use these platforms to get through the level. Since jumping onto the platforms causes them to fall immediately, they have very little time to stall, meaning they must traverse quickly in order to not fall into the abyss below. They must also be careful to avoid the multiple Brick Blocks within the level; they could potentially push the player off due to the autoscrolling mechanic. There are Koopa Troopas and Koopa Paratroopas located in the level as hindrances, though their shells may be used to break some of the Brick Blocks. Upon reaching the end, the player finds a pipe that will take them to the end of the level. A single Boomerang Brother is found behind the exit pipe.
There are two 1-Up Mushrooms hidden in this level. One is found near the beginning of the level, in the middle of a row of three Brick Blocks, and one is found near the end in a single Brick Block that must either be hit with a shell or with Raccoon Mario's tail.