Spoilers for tonight's episode of The Flash are below.
Fans of The Flash knew that some big things were going to happen when Barry, Cisco and Wells took a trip to Earth 2, and tonight’s episode definitely delivered some interesting visuals. But while some of them were expected, such as Barry and Iris (of different Earths) being romantic, there was one that came completely as a surprise: Supergirl in the Speed Force. Check it out.
This is our first concrete visual evidence of the upcoming crossover between the two superhero series, and one that admittedly seems like an obvious decision for the creative team. But news of the crossover only became official fairly recently, and presumably long after the episode had finished filming. It was obviously an effect added after the fact, which is probably why it's such a generic shot of Melissa Benoist's Supergirl flying, but it's still pretty incredible that they went through the effort here to plant the seeds for the network-crossing team-up, and it's cool that CBS wasn't wary of allowing their character to be shown on the sister network.
This moment also tells us something that a lot of comic fans have been suspecting, namely that the Supergirl that The Flash will run into will likely be from a different Earth. The crossover episode is titled "Worlds Finest," and the lack of an apostrophe was a big hint that multiverses were in store. Just because this will be an alternate Supergirl doesn't mean that the Earth 1 version can't pop up elsewhere on the TV side of the DC Universe, so we're still holding out hope that the caped heroine will fly to another network at some point. I'm also totally down with John Wesley Shipp, who plays Papa Henry Allen on this show, to reprise his earlier Flash role for the crossover, as also teased in the Speed Force.
Another thing that's kind of nice is that this moment happened in an episode where we got to meet Killer Frost, the villainous double of Caitlin Snow. She was first hinted at back in the Season 1 finale when Flash had his Speed Force visions. (Along with the return of Robbie Amell.) It's a nice way to bookend things, or even to set up how it'll work in the future. Maybe when Barry Allen heads over to National City for Supergirl, he'll get set up with another set of visions leading to the next big appearance. And maybe he can get some advice on how to stop Zoom.
The Flash is set to blend in with Supergirl for the latter's timeslot for the episode on Monday, March 28, on CBS. And you can bet the Flash episode the next night will find a great way to reference what happens on the other series.