The CW has released a third teaser for the upcoming crossover storyline, called “Crisis on Earth-X”. The episodes will air on November 27th and 28th, and they encompass all four of the CW DCU shows. As you can see, it involves a very large cast.
Plus, the CW posted a lot of still images from the episodes, which will probably give away much of the story if you look at all of them. But they can be viewed at Farfarawaysite.com if you aren’t bothered by potential spoilers.