It turns out that the 'Knightmare' scene from Batman v Superman: Dawn of Justice that intrigued audiences and led to much speculation, was a last-minute addition to the movie. The scene is set up like a dream sequence that also doubles as a warning of a possible future in which Superman has turned evil and enslaved Earth.
Stunt actor Richard Cetrone, who served as Ben Affleck's double for the film, revealed the details of the 'Knightmare' scene on the BVS By The Minute podcast. "After shooting had already started, that scene was added," Cetrone explained, contrasting the sequence with the months of prep that was allowed for planning and executing the film's other giant action set pieces, such as the warehouse fight and the final stand between Superman, Batman and Wonder Woman and Doomsday.
The 'Knightmare' sequence sees Batman transported into what appears to be a dystopian reality where the Dark Knight is a renegade, hunted by a group of soldiers under the orders of an evil Superman. Moments before the evil Man of Steel ends a captured Batman's life, the sequence ends, and Bruce Wayne jerks awake, implying the sequence had only been a dream resulting from Bruce's concern about the possibility of Superman someday turning evil.
Bruce is then visited by a version of the Flash from the future, who seemingly tells Bruce that he had always been right about the danger posed by Superman, and implores Bruce to find the rest of the DCEU heroes. The various plot points regarding the details of the 'Knightmare' sequence were meant to be answered in the next film in the series, which was Justice League. However, Zack Snyder had to prematurely leave the project and the hints included in the 'Knightmare' sequence were ultimately never addressed.
Directed by Zack Snyder and written by Chris Terrio and David S. Goyer, Batman v Superman: Dawn of Justice Ultimate Edition stars Ben Affleck, Henry Cavill, Amy Adams, Jesse Eisenberg, Diane Lane, Laurence Fishburne, Jeremy Irons, Holly Hunter and Gal Gadot. The film is currently available for streaming on HBO Max.