Since Barry Allen (Grant Gustin) made his first appearance on Arrow before spinning off onto his own series with The Flash, The CW's DC Comics crossover events have been one of the major talking points for fans of the network's shared superhero universe. Now that Legends of Tomorrow debuted earlier this year - introduced through one of The CW's crossover events - and Supergirl will be joining the ranks of fellow DC Comics series on the network this fall, the "biggest" superhero crossover has already been teased by CW president Mark Pedowitz.
Still, though Arrow star Stephen Amell has offered his own insight into what might occur in the crossover - it will likely take place over four nights and will not be a musical if he has anything to do with it - we know very little of what to expect and how all four shows will come together. Now, new insight from Arrow and Legends of Tomorrow executive producer Marc Guggenheim confirms Kara Danvers (Melissa Benoist) will be a connecting thread of the crossover.
In an interview with CBR during Comic-Con International in San Diego, Guggenheim revealed the basic structure of how the crossover between Supergirl, The Flash, Arrow, and Legends of Tomorrow will work:
"It’s an external threat from outside the shows that will involve Supergirl coming over to The Flash, then Arrow, then Legends of Tomorrow."
Considering The CW's fall schedule - with Supergirl airing on Monday nights, Flash on Tuesdays, Arrow on Wednesdays, and Legends of Tomorrow on Thursdays - it seems the threat will be introduced on the first night, then carried over throughout the entire week of superhero series. Additionally, Guggenheim did not reveal what the threat will be, but since he describes it as "external" it seems we may be able assume it won't be any of the major villains from the shows' respective seasons - even Legends of Tomorrow's Legion of Doom.
So far, there have been two of The CW's crossover events between its DC Comics series; the first featured Oliver Queen (Amell) and Barry Allen visiting each other's cities to fight one-off villains, while the second saw both superheroes team up with members of the Legends of Tomorrow team to battle Vandal Savage (Casper Crump) - effectively setting up the CW's spinoff prior to its premiere. It seems this year's crossover will be a combination of both these structures, offering individual stories for each series that will tie together in an overarching narrative.
That said, it's unclear whether stars of The CW's superhero dramas aside from Supergirl will appear in any of the other series during the crossover event - or if any other members of Team Supergirl will make the jump in the crossover. Plus, it remains to be seen how the DC Comics shows will handle the fact that Supergirl has already been established to take place in another universe within the multiverse, though that may be resolved prior to the crossover or during the event itself. Still with Supergirl as the newest member of The CW's superhero family, it will be a chance for fans to see her interact with each of the network's other shows - and reunite with Barry after their shared adventure in Supergirl season 1.
The Flash season 3 will premiere Tuesday October 4th at 8pm on The CW, Arrow season 5 will premiere in the same timeslot on Wednesday October 5th, Supergirl season 2 on Monday October 10th, and Legends of Tomorrow season 2 on Thursday October 13th.