I didn't read the whole thread, but just wanted to share my experiences with this word 幻獣.
I had free reign to do anything I wanted in International Studies class, so I did Greek Mythology for 1.5 years. On mythological beasts like gryphon, sphinx(they enjoyed hearing about Oedipus Complex! Interesting that this is common knowledge to Westerners, but unknown to most Japanese), pegasus, medusa, chimera, minotaur, etc. I named my Powerpoint presentation as ギリシャ神話の幻獣.