Because I currently lack the time, I am sharing this idea here. If there is a better place to post this, please let me know. (Runouw forums are currently defunct.)
If you are a Super Mario 63 level creator who happens to have some spare time, consider remaking "Bullet Bill Colorful Nightmare" (video link), a very creative and fun-looking level from 2011, because the author Landy25N has sadly not published the code.
I found the following in an old text file about level codes:
##;8S8!&9/d4"$;/bW"&;/bX "';/S@"'1/[C]B]@^?^>ZB ZAWA]A!#//AK"!1C@@"&292V 6V"$2/2M2L($@)yes,SiSdidSit
Does anyone have a clue from which game it might be coming?