Justice League: Crisis on Two Earths/Headscratchers

Owlman walks through Superwoman on the alternate universe theory, citing one planet where humans never evolved. Then towards the end, on earth prime, we are told that every human action splits off another world. Can you see the contradiction here? Why is fish world even a thing, if there are no human actions to change something?
- Likely he just means that decisions as a whole alter things; no fish chose to go out of the water on that planet, ergo no humans. The bit about it being "human action" that changes everything is likely the result of Owlman's own hatred for humanity, combined with the fact that most alternates are changed by human choices.

The concept of an earth prime makes no sense. It's like one particular branch somehow holding the entire tree up.
- or the Trunk...
- It's the trunk. Only by virtue of the Multiverse it doesn't REALLY exist. The moment Owlman decided to travel there a second Earth Prime is created where he did not make the decision to go there.
  - That wouldn't create an earth, but even if it did, it wouldn't matter, because it wouldn't be Earth Prime. It would be extremely similar to Earth Prime, but it wouldn't be the same thing.
  - The thing is Owlman is mistaken. As was already mentioned the moment Owlman traveled to Earth Prime a different Earth was created where he didn't. More to the point he realizes that there are Earth's where humans never evolved and yet are somehow to blame for the problems. There is also the fact that we know in the DC Universe that humans, if not Earth is relatively young. Removing Earth and humans from the equation wouldn't have any effect on anything Martians, Kryptonians, Thanagarians etc,etc have done to shape the universe. Unless Earth Prime works via equal parts alternate dimensions and time travel like in Turtles Forever where apparently destroying the "source material" destroys everything that was built upon it retroactively.
- The most likely explanation to all of this is that you're taking the "tree" and "branches" analogy too literally. Most likely the actual structure of the multiverses is not really comparable to anything at all except itself. Owlman has either found or believes he has found a point in its structure that, if destroyed, will destroy the whole. It doesn't need to be the "main branch" or a "trunk" or the "original world" or anything like that, it just needs to be the Earth that is situated in the multiverse in such a way that detonating it would have catastrophic consequences to the whole. Everything else is just him attempting to put it in layman's terms.

Why is Alt!Chesire evil? Aren't villain and hero supposed to be reversed in Luthor's universe?
- Actually that was Alt!Katana not Chesire.

If every choice not made on Earth Prime sparks a new alternate Earth, then why weren't there dozens of Batmen and Owlmen fighting there in the end?
- Maybe it's because Owlman is unique among Batman duplicates?
  - Doesn't fit with what we're shown. "Every choice" splits the world. Also, there are versions of Owlman that we would find quite pleasant.
  - Because when Owlman made the decision to go Earth Prime he created a second Earth Prime where he did not make that decision. By virtue of every decision we make creating two universes you really can't get to Earth Prime, certainly not without time travel to just go to the beginning.
    - Deciding not to go to Earth Prime wouldn't make another one. And even if it did, it wouldn't' be Earth PRIME.
- Because who's to say there weren't?
Why did Good!Luthor not use the dimensional shifter to save himself and the Jester in the first scene, right after he had gotten the quantum trigger?
- Because the two pursuers were too close. Jester had to buy some time for Luthor to properly escape.
Are Lex Luthors predisposed to be evil or did Lex know about our Earth before coming here? If I was Lex Luthor and traveled to a new dimension I would have gone looking for my double and his hopefully still operating Justice League. Instead he walks into the police department knowing that they'd recognize him and recognize him as an A class villian so the easiest way to get Superman (who back home is evil) is to threaten world domination. He had to have known the situation prior to showing up.
- No, he walks into the police station to contact the Justice League, but the cops pull guns on him and react to him like he was a criminal, so he makes his 'threat' to ensure they call the League. Simple really.
- He knew that his Luthor was a criminal and that the League were heroes already. Its obvious that he has learnt to spy on and spot the differences between his world and others, because Owlman, Superwoman and Batman themselves can do it. Unless Batman didn't know that Owlman and his planet-killing bomb would be going to a dead iceworld and is an asshole who didn't give a damn.
Why is it that, when comparing the differences between this movie and the DCAU, everyone mentions Green Lantern being different but not Aquaman?
- Because overall Aquaman is a white guy who sometimes has a tan but a beard and hair length is not worth talking about. Green Lantern, on the other hand, is at least several human characters.
After seeing the reversed layout of Alt-Lex's organs, why is Superman's first conclusion that he's from another universe? Couldn't he easily be something more "mundane" like an imperfect clone or a shapeshifter?
- Could a clone or a shapeshifter have reversed layouts?
- Yes actually there was a shapeshifter that reversed everything in the people he copied. The reverse organ thing just proved that Alt-Luthor was a different person from normal Luthor.
- Maybe Superman also used his vision powers to scan Luthor's molecules and see that they spun the opposite direction or some damn thing, but the reversed organs was just the most obvious thing he could point out to everyone else.
How did Superman talk in space? Superman can't talk in space. He wasn't wearing a space suit, he wasn't wearing a breathing mask, and he certainly wasn't speaking telepathically!
- Whether or not he can talk or breath in space really depends on the version of Superman depicted. In the DCAU, he can't breath in space and needs a space suit or breathing mask, in the comics, he's been shown to talk and even hold extended conversations with people while in space (The Supergirl Story arc of Superman/Batman comes to mind specifically).
- Even if he doesn't need to breathe, though, there's no way for sound to travel in space.
  - Well then welcome to comic book logic. Hope you enjoy your stay.

I get that Superwoman is suppose to be a Mary Marvel Counterpart rather than Wonder Woman. But then why do we have Mary Mayhem?
If Crime Syndicate is able to give superpowers to normal humans and turn them into made men, why does the Owlman have to rely on his Powerarmor?
- Probably the same reason Batman never tries to get powers even though there are methods in the main DCU where he could get them. He doesn't need them.
  - Oh, but Owlman seems to need them, as he did create a power armor instead of standard suit. So why not real superpowers instead of superpowered suit?
    - Because he felt like using the suit. That's really all that needs to be said. Probably if someone asks him why he uses the suit instead of getting real superpowers, he beats the crap out of them. With his powersuit.

Why is Deathstroke the president? Why did WB puss out on having a not named impersonator like someone looking like Osama Bin Laden? In the book it was Fidel Castro and I thought that was a great concept. Its a pg-13 movie, it feels dumbed down for the audience.
- Using a real-world figure can date a work.
  - Point taken.
- Also, using an established DC character instead of a real world figure is more appealing to some fans.
- Also... uh... Slade Wilson's actually American? I mean it's the world of flipped alignments, not flipped nationalities.