Massive Mushroom Maze

Massive Mushroom Maze is a secret area in Toad Town, found in a basement of a house. It is a large maze made of mushrooms with several Toads throughout it. Upon reaching the center of the maze, the player will find a hidden star. This area's star does not contribute to the Toad star counter.

Theorizing
It is possible this level is the unused 3KINOP level. Toad's name in Japanese is Kinopio, and seeing as 3KINOP is a shortened version of Kinopio, and Massive Mushroom Maze is themed around Toads and mushrooms, it is very likely that this level is 3KINOP.