[quote=@Lucky]
So we can be effectively any mythical creature? Or just the ones you named?
[/quote]

Yes! You can be any mythical creature as long as you're able to work it into the story of living in a world where humans don't know they exist. You can also change the physical appearance of a creature as well. Let's say you wanted to be a Phoenix. Traditionally the phoenix is a bird, but you could change it so that the story is the phoenix was a human with bird like features. In the tradition of orally passing down stories, the phoenix became a bird instead of a human with bird like features. Once it was written down the phoenix was a bird that's what it stayed as.

I hope this helps!