That power-up is a complete PITA. The yukkuri mushrooms are also frequently used for evil in some later stages. Yukkuri Marisa isn't easy to control (you can't easily stop, for starters) and the mushrooms will chase your ass, so naturally the developers hid them in some item blocks in areas where you wouldn't need or expect the yukkuri shroom.
On another note, yukkuris are also in The Genius of Sappheiros. They're basically that game's metal slimes. (Youmu also learns a skill called Slow Cut. "Cut it easy!")
The family was mugged. When the family was performing the money was actually kept in a Marisa's hat instead of a can, and anon mugged them when they went into the alley.
Unfortunately, it looks like the shithead was the recipient.
That said, it feels like I'm missing something when I read post #28282 and then this page...in the former the Father Marisa says it lost its hat and the flashback says it used it to cover the entrance to the nest.
Well, there is Anko1562 where Miss managed to make the Reimu realize she was a Deibu (Miss' coworkers had said Miss acted like one which is how she brought the subject up with the Reimu).