In Russian mythology there is an interesting character - Царь Кощей Бессмертный. He posesses magical powers and is an antagonist to Иван Царевич or other hero from the mortal world. The name Кощей has interesting etymology. Many people think that it comes from word кости (bones), maybe because Кощей Бессмертный is usually depicted as having skeleton-like look - hairless head, greyish skin color, clothing or armor that depicts bones, etc.
Though there are theories that the кощей is in fact comes from кощун, кощунство. Nowadays these words mean blasphemer and blasphemy accordingly, but it had different meaning before Сhristianity. There are examples of usage of word кощюн as a translation of greek word mythos in a book by Срезневский, so possibly кощюнник would be a person that tells such myths. (There are many claims in the Internet that кощюньник was also a wizard according to him, but I could not find proofs for them in the book).