4) He Makes His Presence Felt In Justice League
Jared Leto visiting London a few months back led to speculation that the actor may have been there shooting a cameo in Justice League. There were obviously theories that he would show up in Batman V Superman: Dawn of Justice (which didn’t happen), but seeing as the Dark Knight appears to be the focal point of this team-up movie, it’s possible that the villain could appear in some form.
The most logical idea would be to have him show up during a flashback, perhaps during a scene featuring Batman and Jim Gordon reflecting on a past encounter with the insane gangster. A more unexpected approach to this appearance could be a scene featuring The Joker crossing paths with Lex Luthor. Those two have teamed up a fair few times in the comics books (often not with very good results), but with the Ultimate Edition of Batman V Superman revealing that the Caped Crusader has sent Lex to Arkham Asylum, it’s possible that they could end up meeting.
However, with Steppenwolf set to serve as the big bad – before Darkseid presumably appears in the sequel – throwing those two in the mix might be a bit much, so we’ll stick to a flashback.