In the third and last Bowser stage (World 3-1) of Paper Mario: The Thousand-Year Door, there is a yellow block that is surrounded by unbreakable grey blocks and seems to be impossible to break.
If Bowser is large or huge, he still cannot break the grey blocks protecting the yellow one, and his flame-breath does not reach the yellow block.
If Bowser is small enough to fit under the grey-block shield, his flame-breath is too weak to break it, and there is not enough room to jump on it.
(To be clear, I have tried all of the sizes that Bowser can be.)
What the heck is in that block and how do you break it‽