When Supergirl premiered in 2015, its placement on CBS worried many fans that the Girl of Steel would never join forces with The Flash and Green Arrow. Despite sharing producers and being owned by the same company, the logistics of a crossover between Supergirl and any of the other shows seemed like a massive challenge. Luckily, they made it work, as the Flash hopped his way over to National City to team up with Kara in Season 1's "World's Finest." The episode was not only a blast, but proved Supergirl took place on one of the many parallel Earths of the Multiverse. Soon, they'll be re-teaming to tackle the Music Meister, and we learned just today that Iris West will play a central role in the conflict.
Meanwhile, Supergirl has supporting characters of its own to flesh out. While Cat Grant won't be returning anytime soon, former-Lois-Lane Teri Hatcher will be playing a villain in an upcoming episode. Not to mention, there's the whole snafu with Jeremiah Danvers, who may or may not be evil. With so many storylines and characters, it makes sense that the prodcuers and writers of Supergirl and the other Arrowverse shows aren't constantly thinking about crossovers. Well, at least not all the time, as it was recently revealed that a true four-show team-up would likely come next year. Many fans have wondered, however, whether we'd see alternate versions of characters like Barry and Oliver on Supergirl's world, or vice versa. For now, it seems that's not in the cards.
Following up his statement a few days ago, producer Andrew Kreisberg explained to IGN why we haven't seen doppelgängers of the other heroes (aside from the Earth Two versions of the characters) on any of the shows.
“The problem with that is it feels to us like if we do that once, we’re going to open the floodgates of insanity. It’s like Supergirl’s over here, and it’s its own show. Technically speaking, it’s just another Earth, the same way Earth-2 is or Earth-3 or Earth-19. So technically speaking, there should be an Alex Danvers on Earth-1, or Earth Prime. But if we start doing that, I just feel like… Not that all hell hasn’t broken loose already, but unless we had a really good story for it…”
The "floodgates of insanity" phrasing mirrors what Kreisberg has previously said about the subject, and he makes a good point. While the comics have never shied away from alternate versions of characters, it can get repetitive on TV (not to mention exhausting for the actors). Still, Kreisberg says the benefit of actors getting to embody different versions of themselves is still possible even without bringing in parallel Earths (these are comic book shows, after all):
“The more you start to do that stuff, the more it can very easily become annoying or like, ‘Here we go again.’ Even on Supergirl itself, like Chyler [Leigh] got the opportunity to play a White Martian [impersonating Alex]. Already built into our show, there’s already characters playing different versions of themselves. It could very easily spiral out of control.”
All of these comments should be taken lightly, of course, as the Arrowverse producers frequently change their mind. At one point they even swore metahumans would never show up in Star City, and we all know how that's turned out. On top of that, the parallel Earths of the show have already given us multiple doppelgängers of Team Flash, not to mention Laurel, whose Black Siren version has shown up on Arrow.
There's also a character like Mr. Mxyzptlk running around in Supergirl's universe. With the interdimensional imp involved, there's a variety of fun ways that alternate versions of various characters could appear. In the meantime, Supergirl will have plenty of new faces to fill its ranks. Today, it was announced that iZombie star Rahul Kohli will be appearing on the show as the mind-controlling villain Biomax. The Girl of Steel is certainly going to have her hands full for the time being.
Supergirl continues Monday, March 6 with ‘Exodus’ at 8 pm on The CW.