According to Guillermo del Toro, the actual working title of the movie is Dark Universe, and it will feature Swamp Thing, Etrigan the Demon, Constantine, The Spectre, Deadman and Zatanna Zatara. There are also one or more mystery characters that Guillermo del Toro refused to reveal, because it would give away the plot.
Guillermo del Toro also revealed the he is writing the outline, and he has already gotten a very good writer to accept the project. Guillermo del Toro describes the writer as the "perfect guy for the job." Guillermo del Toro added that Warner Bros. was already galvanized before The Avengers to launch the Justice League and make their universe cohesive.