In 2012, it was rumored that Pacific Rim director Guillermo del Toro was working on a Justice League Dark film titled Heaven Sent. It would feature Deadman, The Spectre, Swamp Thing, Constantine, The Phantom Stranger, Zatanna, Zatara, Sargon the Sorcerer and Etrigan the Demon. In January 2013, he confirmed that he is working on such a movie, with the working title, Dark Universe, and is hiring a screenwriter for the film. Del Toro revealed Swamp Thing, John Constantine, The Spectre, Deadman, Zatanna and Zatara were characters in the story.

In March 2013, del Toro gave an update that the story bible was complete and he hoped to start the screenplay soon. Production would begin after his next project, Crimson Peak. The film's story would center around John Constantine recruiting Swamp Thing, Etrigan the Demon, Deadman, Spectre and Zatanna. The film would not be an origin story, with each character already established and elements of their backstory coming into play throughout the film. Del Toro also revealed that Floronic Man will be in the film. In May 2013, del Toro revealed that his script features Constantine, Swamp Thing, Madame Xanadu, Deadman and Zatanna as the team, with other "in the mix".

"The route we’re going is Constantine is our lead. Constantine is the guy who leads us in and out of the plot. We have Swamp Thing, Etrigan, we have Zatanna, we have—I will spoil it—the Floronic Man. We have stuff that those who love the darker side of the DC Universe are going to appreciate, and we’re trying to be true to the origins of the characters."
And just recently, Guillermo del Toro revealed that Justice League Dark could fit into the Man Of Steel universe. He further explained that not only is a Justice League Dark movie in development, but it’s what he describes as “very active” development.

“Justice League Dark is very active. I’m doing one more revision while we wait for the writer. It’s somebody big, [and] we’re patiently waiting for that writer. I think it’s worth it, I think it’s a guy we all admire. I’m doing my revisions on my sort of Bible, on my story for the film. I can tell you it’s the writing project I’ve enjoyed the most in English. Devil’s Backbone and Pan’s Labyrinth are in Spanish, but of all my writing and screenplays, this was so much fun because it was character. It was a pretty easy plot, but the character interaction, Swamp Thing with Deadman and Demon, it’s so joyful for me to write that. Constantine is such a great character, so dry. I think it could be a great movie. I don’t want to do many changes until the proper writer comes onboard.”
Courtesy of: Wikipedia, ComicBook, ComicBookMovie, and Coliider