SPOILER WARNING: The following article contains spoilers for Justice League, in theaters now.
Early in the development stage for Warner Bros.' DC Extended Universe, it was revealed that Justice League would arrive in two instalments. Further down the line, the studio opted to scrap the two-part narrative and make Justice League a self-contained flick. Nonetheless, the DCEU is developing at a quick pace and if Justice League performs particularly well (which, domestically, doesn't seem to be the case), there could be a sequel.
With a gigantic roster to choose from and a huge library of source material to go, there are many, many different directions in which Justice League could go next if a sequel is given the go-ahead. So, what do we think a second Justice League movie would include? Let's explore the options.
Warner Bros. could opt to use some mystical nonsense to bring Steppenwolf back as the antagonist for the sequel, but that doesn't sound appealing, nor likely. Instead, the studio will need to introduce a new villain (or two) to keep things fresh. So, who could they introduce?
Steppenwolf fails to make the three Mother Boxes converge to become the Unity -- an extremely powerful force that he plans to use to conquer the planet -- so now's the perfect chance for Darkseid to finish the job, himself. It's clear that Darkseid has attempted to conquer Earth in the history of the DCEU, and he banished Steppenwolf from Apokolips for being weak. We've seen what Steppenwolf can do, so imagine how strong Darkseid would have to be for him to be considered weak.
Darkseid has been a nemesis of Superman for years (and years) in the comics, which basically means he's the nemesis of the entire League -- making him the ultimate candidate for the Justice League sequel. His main goal is to completely dominate the universe and remove all free will. He's one of the most powerful and intelligent beings in the DC universe, and he's always had a fascination with Earth, so perhaps he could pay the planet a visit, forcing the League to intervene.
The Injustice League
The Injustice League is another highly possible inclusion for a second movie. The post-credits scene sees Lex Luthor hiring Deathstroke to break him out of prison, and when they finally meet, Luthor suggests that they create a League of their own to rival the Justice League. Members of the Injustice League in the comics include Lex Luthor, Black Manta (who's set to appear in the Aquaman movie), Catwoman, Sinestro, the Joker, Poison Ivy and Reverse Flash. This provides a great opportunity for villains to be established in heroes' solo movies before joining forces to rival the Justice League.
In the comics, the Injustice League is formed under the suggestion of interplanetary conqueror Agamemno. He sets out to conquer Earth -- like most villainous aliens seem to do -- contacted Lex Luthor to help him do the dirty work. This leads to the recruitment of the aforementioned villains, and while the comics go off in a weird and wacky direction, the movie could just see the super-powered teams face off against each other.