First "DC Universe" animated film to feature the character of Swamp Thing.
The "Demons Three" who appear at the beginning of the movie are the sons of Trigon and half brothers to Raven in the DC comics universe.
"Justice League: Dark" is the second animated DC animated film with an R rating, though the content is closer to PG-13. It still didn't get an MA15+ rating in Australia like "Batman: The Killing Joke" did which in America was the first R rated DC animated film.
Guillermo del Toro has been producing (and originally directing) a previous live-action adaptation of the "Justice League Dark" comic book under the working title of "Dark Universe." The animated film is based on an old script for "Dark Universe."