One of the scenes of S.T.A.R. Labs shows it to be under Nazi control with a red sky, a possible nod to the previous crossover event, Crisis on Earth-X. See more
While Flash and Supergirl are running and flying around the globe at "mach 7" to slow down the earth, they would need to be traveling in the same direction. However, you can clearly see they are going in opposite directions during these segments. See more
Dr. John Deegan
My name is John Deegan, and I'm from Gotham, a city in grave need of heroes. As a doctor at Arkham Asylum, I did my part by protecting this city from the criminially insane. The world didn't understand my methods, so I worked in secret until, one day, when a cosmic being recognized my potential and gave me the chance to be something greater. Someone greater.
[becoming a Bizarro-ish version of Superman
Now I am Superman.