Yay, mythology!
Well, Celtic mythology was important in some of Niamh's Originsverse -- I think it was Revelations.
https://www.spikeluver.com/SpuffyRealm/viewuser.php?uid=501There's a bunch of Icelandic mythology/folklore in Once You Eliminate the Impossible by yellowb:
http://dark-solace.org/elysian/viewstory.php?sid=5172I'm sure there's more. I might stalk this thread.

Oh, for occasional Egyptian mythology, there are 2 fabulous WIPs:
Hindsight by Toften:
http://dark-solace.org/elysian/viewstory.php?sid=5755Tales from a New Body by OffYourBird:
https://archiveofourown.org/works/13757121/chapters/31615521Oooh, Egyptian mythology also played a role in Sunalso's "Hunger"! I'm afraid this one's locked to users of Elysian Fields, but so worth registering if you're not already.
http://dark-solace.org/elysian/viewstory.php?sid=5201