World 4-Ghost House (New Super Mario Bros.)
From the Super Mario Wiki
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To start, Mario should step onto a striped platform that takes him past a wall. The first Star Coin can be found by going up past the blocks and right to another striped platform where he will find the coin above it. After the platform, Mario should press the ! Switch and go through the door, avoiding the Balloon Boo along the way. To get the second Star Coin, Mario should press another Wall Jump on the first red blocks he sees and go up. The third Star Coin is in the Secret Exit. Then, the player needs to jump on the blocks, past the first door (if Mario goes through the first door, it will take him back to the start of the area), and into the second door. This will take Mario outside, to the Goal Pole.
To access the Secret Exit, the player needs to be Mini Mario. When Mario reaches the area with the second Star Coin, Mario should get onto the pipe, not entering it. Then, he should Wall Jump on the pipe, reaching a faraway door. By continuing to Wall Jump and by going up, Mario will reach the third Star Coin. Going through the door takes Mario to the Red Flagpole.