daria made a thing

It’s really fascinating to me how things created for a single, specific, totally obscure fanfic will spread into broader public consciousness. Like, ‘Alexandria’s Genesis’ is a fake condition made up for someone’s “Daria” fanfiction, of all things, but you still see it pop up around the Internet from people who think it’s real or claim to have it. “Mesperyian” is not a real Greco-Roman goddess and was created for another short fanfiction in 2009, yet you’ll see mythology enthusiasts and pagans talk about her as if she was actually part of an established pantheon.

What are some other examples?