Welp, we all know how much Barry Allen loves tinkering with the timeline.
When the first season of Supergirl aired on CBS, it being on a different network than The CW's Arrowverse didn't prevent it from having a crossover with The Flash. However, in that case, the same people that produce the Arrowverse also produce Supergirl, so it was much easier to do.
An Arrowverse crossover with Gotham would be a whole lot trickier to pull off. Aside from it airing on FOX, the pre-Batman series takes place in its own timeless world, but because Bruce Wayne is not ready yet to don the cape and cowl, we can say it's the past when compared to the Arrowverse.
David Mazouz, the 16-year-old who plays The Dark Knight-to-be on Gotham, thinks a crossover with the Arrowverse is a possibility. "I feel like we could easily do a Flash crossover, because he travels in time now," he explained to Movie Pilot at Heroes & Villains Fan Fest in London this past weekend. "The biggest obstacle before The Flash came out, when it was just Arrow, was that Gotham is set in the past and Arrow was set in the present. We were not in the same time period, so how could we possibly do a crossover?"
"However, now that we know time travel was not only introduced, but widely used in the Flarrowverse with Legends of Tomorrow and The Flash, it's very plausible that a crossover could happen," he added, "because they could come back in time and visit Gotham. I would totally support it. I'm a huge fan. I think that would be awesome."
DESTINY AWAITS - With the deadly virus spreading throughout the city, the search for the antidote continues, as Fish Mooney (guest star Jada Pinkett Smith), The Riddler and Penguin reveal plans of their own. Bruce meets Ra’s Al Ghul (guest star Alexander Siddig) and completes his last task in order to fulfill his destiny, but realizes he can’t let go of his past. Meanwhile, Gordon tries to win back Lee, and past alliances within Gotham City are broken, while new alliances are formed.
The all-new, special two-hour “Heroes Rise: Destiny Calling/ Heroes Rise: Heavydirtysoul” season finale episode of GOTHAM airing Monday, June 5 (8:00-10:00 PM ET/PT) on FOX.
Cast: Ben McKenzie as Detective James Gordon, Donal Logue as Harvey Bullock, David Mazouz as Bruce Wayne, Morena Baccarin as Leslie Thompkins, Sean Pertwee as Alfred, Robin Lord Taylor as Oswald Cobblepot/The Penguin, Erin Richards as Barbara Kean, Camren Bicondova as Selina Kyle/the future Catwoman, Cory Michael Smith as Edward Nygma/the future Riddler, Jessica Lucas as Tabitha Galavan, Chris Chalk as Lucius Fox, Drew Powell as Butch Gilzean, Maggie Geha as the future Poison Ivy, Michael Chiklis as Detective Nathaniel Barnes, Benedict Samuel as Mad Hatter
Guest Cast: Jada Pinkett Smith as Fish Mooney, Alexander Siddig as Ra’s Al Ghul, Camila Perez as Firefly, Nathan Darrow as Victor Fries/Mr. Freeze, BD Wong as Hugo Strange.”