Level 2-3 (Mario vs. Donkey Kong)
From the Super Mario Wiki
The player starts next to some falling bridges, below which are Spikes with RamRams walking along them. On the other end of the bridges are ropes the player should climb to reach a Monchee, which will help the player get across to the Key. After grabbing the Key, the player needs to use a Springboard to reach the falling bridges above. To the left is a 1-Up Mushroom and to the right is the locked door.
In the second area, the player starts below a Nitpicker's nest, which will begin flying and dropping eggs on the player after a short period of time. The second area is made up of several moving platforms and a yellow Color Switch after the third platform. After pressing the Color Switch, the player is able to collect the Mini-Mario by jumping from the first moving platform.