In a world without rights issues, this would be an actual thing already. With sequels. Split into separate parts.
Alex Luthor, an inventive YouTuber, has mashed up various superhero elements from both DC and Marvel properties to create an ultimate showdown that pitches Batman, Superman and Green Lantern up against Thor, Iron Man and Wolverine. And many, many more.
It's visually spectacular catnip for comic book fans so make sure you watch this one in 1080p.