3. A Post-Credits Darkseid Reference
When you get a group of Superheroes like the Justice League together in the same place, your run-of-the-mill Supervillains just arent going to cut the mustard. Even Supermans rogues gallery, who are usually much more powerful than the likes of Batmans, pale in comparison to the collective might of the JLA. Enter Darkseid a powerful God-like enemy who usually gives even the Justice League a toothache, usually likes to target the entirety of Earth as opposed to just one city or hero, and has an army of malevolent aliens at his disposal. Exactly the kind of threat level needed to call the individual members of the League together. Plus, hes arguably one of the Justice Leagues most well-recognised rogues, and even just a 15 second reveal of that charcoal mug post-credits as he devises a dastardly scheme would be enough to have me putting the ticket fee aside in advance (although Ive already done that in all honesty). Maybe this is asking a lot; itd require Warner Bros. to have settled on Darkseid as a JL movie antagonist already, but hey, maybe they have. At this stage, we just do not know, but we most certainly can fantasise.