what should be in first teaser trailer for four night crisis that is coming this november.

that would make one hack of good trailer

I think you need to intro the villains first. I don't know much about the villains, but here's a few possibilities:

1. If the villains look like our heroes, then have them in a van or something (I'm thinking Arrow team) and make it look like they're prepping for a mission, but when they arrive and the doors burst open they doing bad things, e.g. killing civilians/resistance fighters or something and reveal how they're evil.

2. Similar to #1 but Supergirl focused, do a night scene of what appears to her (just show cape or boots or from behind or something) flying around listening for trouble, then she hears something and flies in and you see her face, which is the villain, and she starts doing bad things like #1. Flash could work similarly, but getting reports in his earbud/suit from his team.

3. Make a series of alternate intros with an evil/fascist twist for each of the shows featuring their villain counterparts, as if the shows had been made on Earth X, something like what Star Trek: Enterprise did in the In a Mirror, Darkly episodes.

4. Similar to the poster, start by showing Barry and Iris at their wedding and have the villains show up and start tearing up the place. Could even be in slow motion, music playing in the background, showing how the happiest day turns into the worst day.