Lastly, I would not limit the question to creatures only. Much of what is found in the KHM can also be found in myth. For example (and in no particular order) - the cutting off of horses heads (Falada) -horse heads were considered to protect from enemies. Some houses today still have horse heads on their gables. That speech continues to live in Falada's head is as with Odin and Mimir who councils him after his head is cut off. The arguing of giants regarding the division of treasure, etc., etc. Characters often go over or into water to reach the "other realm," the "other world." This might go back to the idea that the realm of the dead was underwater at the bottom of rivers, lakes, and oceans. Frau Holle can only be reached when the girl falls down into the well. The Undying Lands, home of Tolkien's elves is also reached by going "over water" as I recall.