The villain will be Doctor Destiny
- Well The Monitor did give that book to John Deegan who Doctor Destiny's identify out of costume and he does have an antagonist role so I'm going with a yes here.
The Crossover will be set on Earth-38
Word of God more than implies this. It would also give a nice focus on the Earth-38 characters since they always get the short end of the stick in crossovers. Superman and Lois' appearances heavily suggest this too. Plus promotional materials heavily suggest that Barry and Oliver will be the only heroes from Earth-1. Bonus points if the upcoming Batwoman (2019) is confirmed to also exist on Earth-38.- Jossed majority of it takes place on Earth 1
Flashpoint will be referenced
If the versions on the advertisement poster of Oliver Queen and Barry Allen are indeed from Earth-1, and see the situation they are in the first thing that would most likely be assumed to have happened is that Barry time traveled again and caused the switch to happen.- Confirmed it's mention in passing
The switching of superhero identities was also something that was joked about prior to the airing of the flash season 3.
Batwoman will be from the Nolanverse.
Supporting evidence:- At least one character from outside the traditional Arrowverse (Barry Allen from the 1990 The Flash show) has already been confirmed to appear.
- Gotham City scenes were filmed in Chicago, which was also used to portray Gotham in Batman Begins and The Dark Knight.
- It would neatly explain Batman's probable absence.
- Multiple people have pointed out that the CW Batwoman cowl bears a (perceived) resemblance to the one worn by Christian Bale. Perhaps that's not coincidental.
- Jossed. Batwoman has been confirmed to be from Earth-1.
Batwoman will be compared to Alex Danvers.
Kara will mention her sister to Kate Kane and say she reminds her of Alex.- Jossed. The two aren't compared to each other by anyone and she's honestly fairly different from Alex.
The Earth-90 Barry Allen / Flash will perform the iconic Heroic Sacrifice from Crisis on Infinite Earths
As much as we love him, we just can't have two Barry Allens who are both The Flash, and the current one is obviously gonna stay.- Jossed, he's sent basically to the unknown by the Monitor.
- However, Barry was destined to perform the famous sacrifice until Oliver convinced the Monitor to change things.
- Not Jossed. It just happens next year instead.
The Black Suit Superman is not the Earth-38 Superman but rather Superboy-Prime
The final post of the crossover has two Supermans: the regular red suited one and just above him and to the left is the black suited Superman. Superboy-Prime would wear the black suit with short hair after Infinite Crisis and first appeared in the first Crisis that featured The Monitor, who will play a major role in this crossover. Finally, the blacksuit Superman is seen flying above a red sky, hinting that the crossover will homage Crisis.- Jossed. He isn't either of them. It is simply the form Deegan gives to himself the second time he changes reality.
There's going to be a Brick Joke involving Lois and a hammer
Lois is shown on the poster for this Crossover holding a high-tech-looking hammer, and in Hour One, she wields a regular hammer defensively against Oliver and Barry when they suddenly pop into the Kent barn from Earth-1.- Major confirm in Part 3
This is going to result in world's merging.
At least Earth-1 and Earth-38. Considering Black Superman is on Earth-1, and from the trailers we know that Alex will be in S.T.A.R. Labs. So maybe those are hints/precursor that the Book Of Destiny, or the Crisis the Monitor talked about, will change the Multiverse. That's how we'd get Supergirl/Batwoman: World's Finest, and not Worlds' Finest.Also, while I'm not super up on my comic lore, Psycho Pirate is in this as well, and didn't he have something to do with a Multiverse-changing crisis?Furthermore, Flash-90 mentioned realities collapsing as the crisis Monitor is preparing for.- Jossed. Superman-Black is Deegan, Alex is Earth-1's Alex, and things return to normal. However, there's the possibility that....
The 2019 crossover will cause the merger.
It is, after all, the big one: Crisis on Infinite Earths.- It did indeed.
Earth-90 and the other Earths visited by The Monitor were repaired after they failed his test.
But no one remembers. Except maybe Earth-90 Barry Allen.