Warning: spoilers ahead for the latest episode of Supergirl.
The CW has built a small empire of superhero shows, starting with Arrow in 2012 and growing to include The Flash, Legends of Tomorrow, and Supergirl. The "Heroes v. Aliens" crossover event between all four shows just kicked off with Supergirl as Barry Allen and Cisco Ramon hopped universes to visit Kara and ask for her help in battling aliens. The rest of the crossover event will take place on Earth-1. According to Supergirl executive producer Andrew Kreisberg, however, the events of the crossover will have an impact later on in Season 2. He shared this tease about what's to come:
Ever since news broke that the Dominators would be the big villains of the four-part crossover, the stakes have felt somewhat lower for Supergirl than the other three shows. After all, this would be a crisis on a singular Earth, and Kara's pals in her universe were going to be spared the Dominators' assault. Andrew Kreisberg's reveal at a screening for the "Heroes v. Aliens" event (via ComicBook.com) that the Dominators will pose a direct threat to Supergirl later in Season 2 could mean disaster for Kara and Co. in the not-too-distant future. The big question now is of just which Dominators will visit Supergirl in the coming months.
There are two major possibilities. The first is that the Dominators who turn up on Kara's Earth will be the same that Kara helps fight in "Heroes v. Aliens." They're arriving on Earth-1 in the crossover to exterminate the scourge of humanity (a.k.a. metahumans), and their threat will clearly be grave enough that Barry will risk jumping universes to recruit Kara. It stands to reason that Kara's powers will be instrumental in the good guys of Earth-1 saving the world. If she is the game-changer, and if the heroes drive the bad guys away without wiping them out, the surviving Dominators may come to consider Kara a nemesis. They could find a way to jump universes and visit her Earth to enact revenge for her efforts on Earth-1. Barry and Cisco were able to pop into her Earth after only a few tries in the latest episode; surely an advanced race of aliens could manage to cross universes in pursuit of vengeance.
The second possibility is that the Dominators who face Kara in Supergirl Season 2 will be entirely unrelated to the Dominators who assault Earth-1 in "Heroes v. Aliens." The CW's version of the multiverse has made the point that there are many different Earths that are very, very similar to one another. It would make sense if two different versions of the Dominators came to the same conclusion that metahumans deserve to be extinguished. If Kara opposes the Dominators from her own universe, she could have a distinct advantage. She would already know what it takes to defeat them, and she wouldn't even need to pull Barry and Oliver away from Earth-1 for backup. A plan could already be in place to defeat them, and it wouldn't take three episodes of trial and error to figure it out.
We'll probably have to wait a while before we find out just what will bring the Dominators to Supergirl Season 2. Luckily, we'll see a whole lot of them in the meantime. The "Heroes v. Aliens" crossover event continues on Tuesday at 8 p.m. ET with The Flash, then moves on with Arrow on Wednesday at 8 p.m. ET, then comes to an end with Legends of Tomorrow on Thursday at 8 p.m. ET. Supergirl airs on Mondays at 8 p.m. ET on The CW.