And real supernatural mythology, too - the film set in Japan featured real Japanese yokai, folklorish monsters, instead of the usual made-up stuff that Hollywood trots out.

It still cracks me up that, no sooner had you wondered whether we'd get that one-eyed umbrella monster, than the animators promptly delivered. My personal favorite would probably be the Kappa that shriveled up like a Fiji Mermaid after Hellboy dangled it upside-down and drained all the water out of its head. :-)