We talked about this before with Brainiac but

Brainiac should’ve been the villain for JL. Lex Luthor should’ve signaled Brainiac from the Kryptonian ship. Similar idea from Zod when it connects to the codex except he wants to make Superman his pawn while collecting a city on Earth and destroying it. The thing about the codex though is that it is the key to access the Source. The only way to get to the Source is by traveling through the multiverse, getting pass The Fourth World which “would have been” his next plan. So basically Injustice 2 Brainiac. Brainiac could’ve hinted through dialogue and his plans for potential future films that would involve Flashpoint, Crime Syndicate, and New Gods. Brainiac could’ve been the one to open ideas for audience to talk about.