Inside the Fountain

In certain personalized copies, the courtyard can contain a secret area similar to the 4th floor and floor 2b. This area being seemingly inside, or rather underneath the fountain. To access this, Mario must ground pound inside the fountain, which will break it open and will take him to this area. Although this must be done by ground pound on the edge of the fountain. Once in the fountain more levels will open up, Strangely, there is no Bowser level inside the fountain. Here are some of the levels that appear here. There is only one level that can be accessed without the game crashing upon entering. The crashes are likely due to Nintendo scrapping this area early in development.

Gusty, Gusty Greenhouse
The level appears to be a giant Greenhouse. The level itself has a wind mechanic similar to tall tall mountain. However, there is not much to not about except for a few things, There appears to be an unused sunflower NPC that looks similar to Amazy Dayzee from Super paper Mario. For an unknown reason, Mips appears in this level, possibly for a star. Finally, upon collecting the level's first star, which is atop a giant sunflower, the game crashes, and for whatever reason, the area inside the fountain can no longer be accessed.