Batman v Superman: Dawn of Justice.
The challenge is the studio never wants one adversary to triumph over the other, upsetting fans of the losing hero and risking interest in future movies.
So along comes a shared adversary.
Batman v Superman.
BUILD A UNIVERSE
The hugely successful Marvel Cinema Universe franchise started with standalone movies about Iron Man, Hulk, Thor and Captain America.
With years of planning, they all built towards the Avengers movies, with the climactic
Avengers: Endgame also involving characters from the
Guardians of the Galaxy movies.
The next phase, starting soon with
Black Widow, brings in new characters.