I can't remember where I heard it but the line "in an infinite universe, everything that can exist must exist" has stuck with me. Since you mentioned fiction, I've been wondering if our experience of different stories through different media constitutes something "existing". For example, maybe the events in the Star Wars saga don't have to be literally happening, or have happened, in the same way our reality appears to be playing for us. Since all is "mental" (the Kybalion is an interesting book i think you would jive with), then the mental activity of consuming the story and playing it within our minds counts as having "existed".