Episode 21 scared the crap out of me when I was a kid. Even now, I think it's a really weird episode. It has such an eerie atmosphere to it, and the episode barely uses any BGM, which causes more of an uncomfortable feeling. And I remember it being weird to see Hayate get so messed up. :laugh:
The episode's writer, Michiru Shimada, is a big anime writer from what I've read, and this episode is the only episode of not just Flashman, but any toku that she ever wrote for. I've always imagined that the Flashman staff saw this episode, freaked at how screwed up the content was, and was like "Ooooooooooookay, we'll call you, don't call us."