The LEGO Batman Movie director Chris McKay revealed the plans for a cancelled sequel penned by Rick & Morty co-creator Dan Harmon and Loki head writer Michael Waldron
"Dan (Harmon) and (Michael) Waldron had done a first draft of the script that was really great. It was truly epic... both from an action standpoint and from a story standpoint," said McKay, speaking in an interview with Collider. "The structure was Godfather Part 2... a story about Batman’s relationship to the Justice League (and Superman) now as well as the formative moments of the Justice League (and Batman’s relationship with Superman) then."
Responding to the interview on Twitter, Waldron said he "loved this project" and posted the sequel's title page.
Released in Feb. 2017, The LEGO Batman Movie features Will Arnett as the voice of the LEGO universe's Caped Crusader, an emotionally unavailable superhero who learns to open up and work with others. According to McKay, the sequel would have evolved the film's themes about friendship while exploring "how hard it is to change [and] to commit to change... Especially when maybe you weren’t such a good guy to your friends. Your old friends might not be able to see the new you. They might still live in the past. But as the movie (and Robin) finds out... the past might be more complicated than it seems."
Moreover, McKay said Lex Luthor and OMAC were lined up to serve as the film's villains and teased "a big crossover at one point in the movie that you can only do in a LEGO movie." This would've marked the second appearance by Lex Luthor in the LEGO universe following his cameo in 2019's The LEGO Movie: The Second Part, where he was voiced by Ike Barinholtz. As for OMAC, McKay didn't specify whether he was referring to One-Man Army Corps/Buddy Blank -- a futuristic superhero created by Jack Kirby in 1974 -- or Observational Metahuman Activity Construct, the sleeper cyborg assassins controlled by a satellite created by Blank and Batman.
Prior to The LEGO Batman Movie's critical and commercial success, McKay admitted Warner Bros. was "leery of LEGO Batman being an actual Batman movie so I was constantly told to hold back... I would have quadrupled down on making [the sequel] as much of a real Justice League movie... as humanly possible." However, with Universal having secured the rights to produce new theatrical LEGO movies in 2020, he no longer expects the sequel to happen.