You can mix and match things when you're talking about mythical creatures, that's how new myths were created. If you want to be technical about the myths themselves and their origins though, this text is a great help if you are wanting to create something like that. I bought this particular book years ago and it's a good reference/starting point:
http://www.amazon.com/Giants-Monsters-Dragons-Encyclopedia-Folklore/dp/0393322114
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Still smilin'
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