While Zack Snyder's Justice League is mostly the unfinished cut that Snyder had developed during initial production of the film years ago, he did film four to five minutes of new footage when he was given the go-ahead to finish his cut of the film, making up the new Knightmare sequence that involved a conversation between Bruce Wayne/Batman (Played by Ben Affleck) and Joker (Played by Jared Leto. Affleck, Leto, Amber Heard, and Joe Manganiello returned in those additional shoots to reprise their DCEU roles as batman, Joker, Mera, and Deathstroke, respectively, but the scene also required Ezra Miller as Barry Allen/Flash. This presented the biggest challenge as Miller was filming the third Fantastic Beasts film (2022) in London at the time Snyder was doing additional photography.
To pull off directing the scene, Snyder sent crew drawings and diagrams of how he wanted the scene to look. Snyder's video feed played through a stand on a table enabling him to direct Miller and the crew, who filmed the scene on his behalf. Amazingly, Snyder managed to create a seamless sequence of all the characters involved (in addition to shots of Ray Fisher as Victor Stone/Cyborg). Stay tuned!