Development and writing[]
In February 2019, it was announced that an animated adaptation of the miniseries Batman/Teenage Mutant Ninja Turtles was in development, as a collaboration between Warner Bros. Animation and Nickelodeon. In May 2019, Jake Casterona was announced to be directing from a screenplay by Marly Halpern-Graser, with Ben Jones producing; he previously worked on both Batman: The Brave and the Bold (2008-11) and Teenage Mutant Ninja Turtles (2012-17).
Early during production, Jones wanted to omit the interdimensional aspect of the original comics, due to both his love for crossovers such as Superman vs. Spider-Man that established both properties as existing in the same reality, as well as simplifying the story. Due to this, Halpern-Graser sought to instead stay faithful to the comic's tone and structure while incorporating these changes to the story, with multiple lines and panels being adapted verbatim to the film. Regarding the portrayals of Batman and the Turtles, Casterona wanted to contrast them by portraying Batman as more serious and the Turtles being more lighthearted and fun-loving. However, he wanted to avoid portraying them in a goofy light similar to the 1980s series, so he and the crew instead drew inspiration from the 1990 film and how it portrayed the Turtles in a lighthearted manner while still being serious in tone. Producer Ben Jones and screenwriter Mary Halpern-Graser expressed interest in a sequel that centers on Batman interacting with elements from the Turtles franchise, expressing particular interest in featuring characters such as Krang and Bebop and Rocksteady.
Casting[]
The initial announcement revealed Troy Baker would reprise his roles as both Batman and the Joker from previous DC properties, making Baker the first actor to portray both characters in the same property. The film features Darren Criss, Eric Bauza, Kyle Mooney and Baron Vaughn as the four Turtles: Raphael, Leonardo, Michelangelo and Donatello. Rachel Bloom voices Batgirl and Cas Anvar voices Ra's al Ghul. In addition, Tom Kenny, John DiMaggio, Carlos Alazraqui and Tara Strong reprise their roles as the Penguin, Mr. Freeze, Bane, Harley Quinn and Poison Ivy from various DC properties. Other key cast members of the film were revealed a month later, which consists of Ben Giroux as Robin, Andrew Kishino as the Shredder, Keith Ferguson as both Baxter Stockman and Two-Face, Brian George reprising his role as Alfred Pennyworth from Batman: The Killing Joke, and Jim Meskimen as both Commissioner James Gordon and the Scarecrow. Voice recording had begun by the time the film was announced. Both Warner and Nickelodeon were involved in the casting process, while Gene Vassilaros serves as casting director, after working on that role in previous animated Turtles media. According to producer Ben Jones, Nickelodeon executives mandated for none of the cast members from the then-current series Rise of the Teenage Mutant Ninja Turtles to be brought back to reprise their roles.