Fables And Fantasies

I think that Poul Anderson's causality violation/historical alteration caused not by extra-temporal intervention but by quantum fluctuation was an original contribution to time travel fiction. Usually, imaginative authors present new treatments of familiar ideas.

Familiar Ideas
(i) Exotic beings hide among us.
In Poul Anderson's works: aliens; "a-mortals"; futurian time travelers.

In Bill Willingham's Fables, fairy tale characters are disguised as "mundanes" in New York. A journalist who discovers this clandestine community of ageless people thinks that they are vampires.

(ii) Alternative Earths in parallel universes; what is fiction on one Earth may be real on another.
Poul Anderson: several novels and short stories.
Fables: the "Fables" are exiles from other Earths somehow based on or derived from the mundane Earth.