Warner Bros. Animation is apparently working on an animated feature film adaptation of the "New 52" series Justice League Dark. The title is mentioned in a listing of extra features for Batman: The Killing Joke with the British Board of Film Classification. Warner Bros. Animation commonly has a short clip of its upcoming DC-related animated films in its home video releases.
It is unknown if this presumptive Justice League Dark animated feature is related in any way to Guillermo del Toro's long-simmering live action adaptation. First mentioned in January 2013, del Toro has been very public about the stop-and-start developmental process he's had with Warner Bros. Pictures over the film. In April 2015, the writer/director stated he had turned in a final draft of his script for the project, and would direct it if he and Warner Bros. could agree on a schedule, but he would be open to someone else directing it as well. No mention was ever made about del Toro's Justice League Dark being an animated film, however.
DC Comics' Justice League Dark series launched in 2011 as part of its rebooted "New 52" comics line, and ran for several years. A second volume, titled "Dark Universe," by James Tynion IV and Ming Doyle, was announced in early 2015 as part of the "DC You" initiative but was never released.
Batman: The Killing Joke is scheduled to be released digitally on July 23.