I wonder if Bill was originally meant to appear in just one epsidoe, and then became a regular character. If you think about it, he sort of looks like a whatnot (is he?). Same with Mr. Poodlepants, Zippety, and Ernest Pleth (though I only recall him appearing in two episodes). I wonder if these characters were made from whatnots, and if any were only meant to appear once (though I doubt it with Zippety. I think he might have been a random whatnot design meant to be used multiple times).