every time Mario gets a power up, we get a lengthy animation of him transforming magical girl style. this would include an awkward closeup of his body as its happening and excessive jiggle physics on his stache.
it is an unskippable cutscene and happens every time.
In Paper Mario: The Thousand-Year Door, Goombella mentions having shoes. Since her sprite uses the same graphics for her feet as all the other Goombas in the game (with only a color change applied), this seems to imply that all Goombas are in fact wearing shoes. However, in Super Smash Bros. for Wii U, Goombella’s trophy shows a new design for her that adds soles to her feet, differentiating them from other Goombas and making them look more like shoes. While this design decision was most likely a coincidence, there is a chance that it could have been an attempt to clear up the above quote.
An unused level named “#2 MORTON’S PLAINS” can be found in the files of Super Mario World. It is a functional copy of Donut Plains 1 with glitched graphics. Top: a section of the level. Bottom: the background from the level, horizontally tileable.