The Debug Menu Access Point is a place in Onett where you can access the game's debug menu. To reach this, you must use the skip sandwich to jump a cliff on Onett's north eastern side. From there keep going north east, past the trees until you get to an intersection of two blank blue walls. This can be shown at the right. From there, face north and "Check" the area several times. To the right is also a picture of the debug menu.
Here is a link to a video on how to do this: https://www.youtube.com/watch?v=WIGf6xVaf88