Level 1-1 (Mario vs. Donkey Kong)
From the Super Mario Wiki
In the first area, the player needs to jump onto the blue Color Switch to make a red wall disappear. They then to jump onto the red Color Switch to make the blue wall disappear, gaining access to a Springboard and a "Help" box that shows the player how to use it. Using the Springboard, the player can grab the Key and take it to the locked door, entering the next area.
In the second area, there are four Shy Guys that can be defeated using the Garbage Cans. By climbing the ladder on the left side of the area and moving back to the right side, the player can collect the Mini-Mario. Alternatively the player can get to the Mini-Mario simply by performing a Backflip at the start.