Level 2-2 (Mario vs. Donkey Kong)
From the Super Mario Wiki
The player starts under the locked door, next to a wire and Springboard; either of which can be used to reach the ropes above. Using the ropes to move to the right of the area, the player will find a 1-Up Mushroom and a yellow Color Switch. Pressing the Color Switch will cause two Barrels and a RamRam to fall onto the Spikes below. The player can then grab the Key below the platform they are on and use the Barrels and the RamRam as platforms to reach the locked door.
In the second area, the player starts below some wires, which they need to use a nearby Barrel or a Handstand Jump to reach. Above the wires are ropes the player needs to climb and jump across, avoiding the Spikes, to reach an area with RamRams and moving platforms. By defeating or moving past the RamRam on the left, the player can use a moving platform that leads to the Mini-Mario.