Top Secret Area
(Note: You must have a cape to be able to reach this)
At the beginning of the Donut Ghost House, run to the end of the first platform, then turn around and run back the other way, holding the run button down as you do so to build up speed. Right before you come to the end of that platform (where the level would originally begin), jump upwards and hold the jump button down. You will begin to fly upwards (which is why the cape is needed) and will continue to do so until you fly off screen. Wait a few moments while begin off screen, then turn right and continue to fly right. After you land, continue running to the right and you will eventually fall into a small room filled with one up blocks and a doorway. Enter that doorway and cross the finish line for a level to open up behind the Donut Ghost House called "Top Secret Area". Within this short level, you will find several power-ups lined up and a Yoshi. This level will become an extremely helpful source in the later stages of the game.