You don't want to use the omnium-gatherum in a novel. Lacks unity. OTOH, you often don't want to use them in a game. Many discussions recommend paring them down hard.
But I was thinking in particular of a technique I recommend for the writer: use only monsters from a specific folklore. It tends to still give a certain merry chaos that lends realism, but prevents you from having to deal with issues like -- since the kitsune is hanging out with the fairy folk like one of them, is it vulnerable to iron?
Would be a bit trickier with a DM, I was thinking, since not only are the things not labeled by folkloric origin, they often don't have one, or else they are so far departed from the source that they might as well be. Some things could just be refined: an Eastern European campaign could, instead of dragons, just use dragonborn and call them dragons. Mind you, you have to beef them up, because while dragons can ride horses, dance with humans, and even believe it when they are told they are the same size as the human hero, they are at least as formidable as ogres. But Baba Yaga -- you can't use hags, which are faintly reminiscent of the British folklore they are derived from. You'd have to brew your own, possibly finding a better monster, or giving her a class level. (Sorceress, maybe?)
But, on reflection, that's what you have to do in a novel, picking and choosing what effects you want to give the creature, as plot devices. The big difference between that the novel doesn't need the stat block -- it needs the aesthetic suggestions that let the monster evoke whatever wonders and marvels you need.