Supergirl season 1, episode 18, “Worlds Finest,” brings in The Flash‘s Barry Allen for a superhero team up.
The crossover between Supergirl and The Flash was long rumored before it was officially announced in February. According to Supergirl and Flash executive producer Greg Berlanti at a screening, “We always wanted to do” a crossover. “From the day we cast Melissa [Benoist], the notion of her in scenes with Grant [Gustin], or someday maybe, in the best of all worlds, with Stephen [Amell], as well, it’s exciting to think of them on screen together.”
Berlanti adds, “But, a few things had to go right. We were introducing this notion of Earth-2 and the multi-verse on The Flash, and that had to work. We’ve always said, very openly, that The Flash and Arrow exist in a universe where there’s no Superman, or you would have heard about him. They would have had at least one conversation about him, and certainly Supergirl, as well. That was one thing.
“And then, there was the notion that it’s two separate networks, so it’s more challenging, in that way, because it’s not so convenient. It’s two separate cities that they shoot in. We wanted [Supergirl] to work and stand on its own on CBS, and have its own audience.”
The original plan was to “wait until the second season, but after Christmas, we came back and were planning out the final third of the year and we thought we could do it. It felt like the right time for him to enter her world and help her out. So, it all came together. We went to all of the powers that be and said, ‘I know we indicated that maybe we’d wait a little longer, but we’d really like to do this now,’ and everybody was very enthusiastic.”
EP Andrew Kreisberg adds that the crossover “isn’t just a gimmick episode” because “Supergirl really needed him this week because of the things that she’s been dealing with,” such as her exposure to Red Kryptonite and having both J’onn and Alex go on the run.
Additionally, Berlanti explains that there might be a bit of confusion for Flash viewers; Supergirl and The Flash “flip order because [Supergirl] airs on Monday, and The Flash episode that hints at how he gets over there and gets back airs on Tuesday. The audience will have to forgive us that one is going to air before the other, and they shouldn’t wait to watch Supergirl until after The Flash episode. But, you’ll see the shout-out in the next episode of The Flash. It deals with Barry increasing his speed. I’m very excited about the next episode of The Flash, too.
“That’s one of the things with the fact that it was different networks. Had it been all on one network, we would have been able to coordinate that. I’m actually surprised that we were able to do it as closely as we did, and that it worked out to that degree.”
As for why The Flash was chosen for the Supergirl crossover, Kreisberg says, “The Flash and Arrow cross-overs have always been designed to highlight the hero’s differences. The first one was Flash vs. Arrow. And even in the ones we did this season, when they were working together, there tended to be a great deal of conflict. It’s a cross-cutting of styles and, ‘Should we be doing this, this way?'”
On the other hand, “What was appealing about this was the idea of Melissa and Grant being so similar as actors, and Barry and Kara both have a light to them. They’re definitely heroes that are daytime heroes that live more in the light. Watching the two of them form this instantaneous best friendship was, creatively speaking, part of what was really exciting for us to explore in this episode.”
If those teases aren’t enough to get you excited for “Worlds Finest,” we also have several sneak peeks from the episode: