The Back to the Future films come up more than once in the dialogue of Avengers: Endgame, mostly as an example of the kind of time travel logic that Anthony and Joe Russo’s movie seeks to avoid.
The first references come in the scene where Scott Lang approaches Tony Stark with his initial idea for a “Time Heist.” The two “rules of time travel” listed by Ant-Man – no talking to your past self, and no betting on sporting events – seem directly inspired by 1989’s Back to the Future Part II, before Iron Man mentions the franchise by name when he asks:
“Are you seriously telling me that your plan to save the universe is based on Back to the Future?”
The reference comes back a little later when Scott hears how time travel actually works in the MCU, and realizes that the Robert Zemeckis sci-fi movies are “a bunch of bullshit.” But if a new video shared by Reddit user Malechite (check it out via the link below) is anything to go by, then Endgame also features a subtler nod to the second Back to the Future much later in the film.
The opening third of Back to the Future Part II sees Marty McFly journey to the then-futuristic year of 2015, where he sees a cinema advertising a screening of Jaws 19 on “HOLOMAX.” Towering above the movie theater is a cartoonish hologram of the infamous shark himself, who bends down to take a bite out of Marty before disintegrating into nothing.
Now, jumping ahead to the climax of Endgame, there’s a moment after Tony Stark snaps his fingers where we see a rather shark-like Chitauri Leviathan swooping down towards Rocket. But just when it looks like the creature has Rocket in its mouth, it suddenly turns to dust.
Given the film’s more obvious references to Back to the Future, it’s easy to believe that the callback was intentional, suggesting that while Avengers: Endgame may reject the time travel logic of the movies, it still takes some inspiration from Doc and McFly’s adventures.