When you use the magic potion to get the mushrooms, do not pick up the surrounding vegetables (which are coins in the magic door) immediately. Find the location in each level where there are the most vegetables that are close together. Drop the magic potion and go in the door. Pick up as many coins as possible. Repeat this once, after doing something that will make the potion reappear (such as climbing a vine, going down a pipe, or entering a door).

In World 3-1, take Toad (because of his lifting power). Fall down the waterfall onto the platform where the door is at the bottom. Enter the door and get the magic potion. Drop it anywhere there is a continuous stream of coins. Enter this door, and grab as many coins as possible. Go out the door you came in, then return, and repeat once.