This crossover has so many theories, it's insane.
As we've talked about for multiple episodes, the 5th annual Arrowverse Crossover is coming to our screens within the next few weeks and we've had so many promotional stills that could possibly spoil plot points. However, audience members and fans of all of the shows included in this year's crossover, The Flash, Arrow, and Supergirl, and of course our new girl Batwoman, have many theories about the plot of the reversal of all characters.
The premise of this crossover is that "Arkham Asylum doctor John Deegan rewrites reality, which results in Oliver Queen and Barry Allen swapping lives. In the new reality, they are the only ones that know that they are in the wrong lives and have each other's powers, which results in them going to Gotham City with Kara Danvers / Supergirl to confront Deegan." (Source)
As we've seen in past photos, many of the main characters are in the opposite characters suits. We have yet to see anything like this for Kara, however, we have seen Kal El aka Superman in a black super suit. Which some compare to UltraMan and SuperBoy.
BUT - In the promo above, we see a different Alex...? Alex Danvers is not part of original comics, so when it comes to crossovers, the character of Alex Danvers is free reign when it comes to her inclusion to the plot.
An interesting theory that has been posited about this scene is that Kara and Kal have switched places? Deegan has swapped them; not on earth, but their entire life story. So Alex Danvers swapped also?
The theory is that Kara arrived on Earth at the correct time but did not grow up with Alex and the rest of the Danvers. Kal grew up with the Danvers and Kara was actually taken by the government when she arrived and used a test subject. This theory possibly could lead to why Alex is reacting so negatively to Kara in the above scene because Kal is her foster brother, who we don't know is a protagonist or an antagonist, and she is just an alien that inhabited their earth? Are the Danvers good people in this crossover? Does Jeremiah still work for Cadmus, but Alex AND Kal work for them also?
SO MANY PLOT QUESTIONS.
To see more of these theories, click here.