~Yo-YO, let's GO! PSI Prodigy!~
This was in Paper Mario: The Thousand Year Door and Super Paper Mario. Paper Mario: TTYD's version was more fun and challenging imo. I usually did this after I beat the final boss in both games though, so it was just an extra thing for me. (yes, I know there's already topics on this, but those are like 4 years old). Takes me around 2 hours to finish everytime I do it, regardless which game I'm playing.