When Supergirl was first announced as in development by Arrowverse producer, Greg Berlanti, fans immediately wondered whether the Girl of Steel would crossover with any of The CW's DC heroes - despite her status on CBS. While we have not yet seen Supergirl interact with Green Arrow or the Legends, the powers that be did allow Barry Allen to jump into "Earth-CBS" to help Kara defeat Livewire and Silver Banshee.
When Supergirl's first season came to a close, its future was left up in the air; that is until the series moved over to its current home, The CW. Now, the network is home to four Berlanti-produced DC shows, Supergirl, The Flash, Arrow, and Legends of Tomorrow. And with all four shows encompassing the same multiverse, it did not take long for the announcement to come that there would be a massive crossover featuring characters from each series. It was later announced that Kara Danvers and Barry Allen would also join together in a musical outing.
As for the massive crossover, it was revealed that it would begin on The Flash, and run through the 100th episode of Arrow, before concluding on Legends of Tomorrow. For some time fans wondered what threat would be so great to unite all four shows, but just a few weeks ago, it was disclosed that The Dominators would be the culprit. One of the last remaining questions is how Supergirl would find her way to Earth-1, or vice versa. While there may have been some initial hopes that The Flash's "Flashpoint" arc would have fixed that problem, it looks like that is not the case.
EW is reporting that executive producer, Marc Guggenheim, discussed how Kara would travel to Earth-1 while speaking with reporters during a screening of Arrow and Legends of Tomorrow. “Last year, Supergirl established that Flash was able to make his way to what I call Earth-CBS, and it stands to reason that, with the proper breach technology, the reverse can happen,” said Guggenheim. As for what prompts the heroes of Earth-1 to seek Supergirl's help, Guggenheim explained, "Once the heroes realize that they’re up against aliens, they decide that they need an alien on their side." He added, "Fortunately, Barry knows a really nice one. I don’t think it’s a big shock that between Barry and Cisco, and all their experiences with Earth-2 and the multi-verse, that they can pluck her from Earth-CBS."
One of the more complicated issues (of surely many) regarding the crossover is that it ends up falling during Arrow's 100th episode. It has already been reported that the creative team is pulling out all the stops with regard to the seminal episode, with many former cast members returning. Guggenheim addressed the concern that the crossover could overshadow the 100th episode, explaining, "When the news broke that the 100th episode was also going to be the crossover episode, people were up and down my Twitter and Greg [Berlanti’s] Twitter I think, in this case, in a very positive way." He added, "People didn’t want to feel like the crossover was highjacking what should be a really seminal episode and a seminal moment for the show Arrow, which I think is wonderful. Greg came up with an idea that really does allow us to have our cake and eat it, too."
Further, Guggenheim added, "I haven’t seen the episode all cut together yet, but it has some incredibly iconic moments," he said. "It is a love letter to the show, it draws on all previous 99 episodes pretty much. Everyone who we could have in the episode, from a scheduling point of view, is in the episode. Even the people who we couldn’t have, because of conflicting schedules, are represented. At the same time, you’ve got Flash and Supergirl; that’s an enormous amount of fun. Certainly the recruits also play a very large role, an important role, in the episode. I’m really excited about it."
This is all a lot of information to absorb, but it certainly sounds like the team behind the crossover, and Arrow's 100th episode, have intensely thought everything out, and are planning on delivering one of the more epic three hours in superhero television history. This will be the Arrowverse's second attempt at a fluid crossover, after last year's, which introduced Vandal Savage, Hawkman, and Hawkgirl to both Team Arrow and Team Flash. Prior to that crossover, The Flash and Green Arrow joined the other's show for a one-off episode. Three hours of continuous story is no easy endeavor, but if anyone can pull it off, it is this team.
Supergirl season 2 airs Mondays at 8pm on The CW; The Flash season 3 airs Tuesdays in the same timeslot; Arrow season 5 airs on Wednesdays; and Legends of Tomorrow season 2 airs on Thursdays.