What would happen if all the movie studios and rival comics publishers Marvel and DC put their differences aside and let every single one of their popular film and TV characters have at it in an epic showdown? YouTuber Alex Luthor (cute name) thinks it would look something like this. He craftily cuts together footage from “The Avengers,” “Man of Steel,” Christopher Nolan’s Batman movies, TV shows “The Flash” and “Arrow,” the “X-Men” films — even fan-made trailers for “Deadpool” and “Wonder Woman” — to create the ultimate super-powered mash-up. One thing’s clear, though, when this many superheroes fight, your city doesn’t stand a chance. Also, maybe it’s cheating to include Ken Watanabe from “Godzilla” saying, “Let them fight,” but I’ll allow it. Enjoy this trailer, because it’s for a movie that will never, ever happen. Follow Ned Ehrbar on Twitter: @nedrick