Okay, there is a big spoiler in the trailer for the episode of Arrow called Who Are You? I'll talk about it below the video…
But remember, there are spoilers in the video.
Besides the thing about Adrian Chase talking with Oliver Queen about the death of Billy Malone… We learn a bit about Laurel's return and it's not the Laurel that Oliver knew and loved. This is most likely Black Siren from Earth-2. The last we saw of her she was locked away in the pipeline at STAR Labs, but since Flashpoint changed how metas are locked-up, the fact she's out could be explained a lot of different ways. The key here is that this Laurel has her sonic scream naturally, not through a device made by Cisco Ramon.
This open up a lot of possibilities at this point. Is she coming in as a villain? Is she wanting to find a place on this Earth. Maybe she wants to turn over a new leaf? The sonic scream wasn't something the show could have in the first season because there were no powers. But with the Flash and metas, they can do it now and bringing this Laurel in with a bit of an edge and a chip on her shoulder could be an interesting dynamic.
I find it interesting that they would release that much of a reveal in a trailer. You'd think they would want us to see that live… unless they have something bigger up their sleeve.