Level 2-5 (Mario vs. Donkey Kong)
From the Super Mario Wiki
The player starts next to a RamRam, which can be defeated by dropping a piece of floating fruit onto it. By riding a moving platform upward, the player will find a Snapjaw and a blue Color Switch to the left. After pressing the Color Switch, the player can reach the Key at the bottom of the area, located next to a RamRam and a 1-Up Mushroom. By carrying the Key up the moving platform, the player can unlock the door to the next area.
In the second area, there are several fruits that can be used to defeat the four Snapjaws. The player can reach the Mini-Mario to the right by jumping across the ropes while avoiding the Snapjaws.