That reminds me, I should continue my Shroomish solo on Ruby. :)
Anyway, I had an idea for a challenge, which would have to be based on either the Pokemon Anime or Manga. Simply put, you'd choose one Pokemon to start off with, which you, or someone else can choose. You take that Pokemon, and find it's debut in whatever you're basing the challenge on, and go from there. So if your Pokemon that you start off with was Houndoom, you'd have to find the episode, or chapter which Houndoom debuts in, and then choose debut Pokemon in order from there. After Houndoom's debut comes Murkrow's debut, so you'd have to use that as well, and so on.
Does that make sense? ^_^