It's the second time I've referenced Papillae in my comics, but the first time I spelled it right! Whoops!
Doctor Phage was originally conceived as a character for the Fear Hole, but I've yet to write an episode that incorporates him. He was then reimagined as the star of his own little world where for no real reason he took on creatures from the Mythos. I also considered him as a boss/mentor for Salina and Magdolene, we'll see if that works out.
He really got around without actually being in anything.