Egypt has a great serpent something like the Vikings. Apophis, enemy of Ra.

Floods are real, but several somewhat isolated events packed into a few hundred years. Now if you’d like, there is a terrifying scientificish way for the earth to flood all at once; check out the partially declassified “Adam and Eve story”. I’m not going to attempt to summarize. Albert Einstein thought the author was smart. Good luck, I still spend afternoons thinking about what a weird book it is.