'The Flash'-'Arrow' Crossover: EPs Talk 'Legends' Easter Eggs, Wells' Surprising Alliance

The Flash still 2 - H 2015
Courtesy of CW

[Warning: This story contains spoilers from Tuesday's episode of The Flash, "Legends of Today."]

When Arrow and The Flash debuted the first ever crossover event last year, the showrunners had no idea that it would be anything more than a one-time thing. So when they sat down to plan out this year's two-night crossover run, executive producer Greg Berlanti and co. decided to go even bigger this time around. Instead of just combining the casts and story from Arrow and The Flash, they also decided to throw the upcoming series Legends of Tomorrow into the mix.

Part one of the crossover introduced Carter Hall, aka Hawkman (Falk Hentschel) on The Flash. He is the latest reincarnation of an Egyptian prince who is fated to reincarnate throughout time for centuries along with his soul mate, Kendra Saunders, aka Hawkgirl (Ciara Renee). While Carter can recall all the memories of their past lives, it took pushing Kendra off a roof for her powers to emerge, and her memories slowly started to come back. But their story will continue in Wednesday's Arrow episode, as immortal villain Vandal Savage (Casper Crump) follows the Hawks from Star City to Central City.

Of course, introducing Legends of Tomorrow characters provided a new set of challenges for the crossover, logistically-speaking. Arrow executive producer Marc Guggenheim recalled one meeting in which a whole room of assistant directors tried to make the schedules for all three casts for the crossover, which resulted in everyone "bleeding from the brain," he joked.

"We had already started to shoot the first couple of episodes of Legends before we shot these episodes," Berlanti told a small group of reporters after an screening of the crossover. "We also knew that there were characters who had been on Flash and Arrow that we were also shooting out of those respective shows before we went into shooting Legends to then have to come back and do the introduction of some of the characters here.

"So it was about as out of order as you can imagine and most of it happening concurrently," he continues. "There were a lot of conference, logistical sessions of, how can we, on a basic, basic level, pull this off? Let alone make it interesting and entertaining and coherent."

But that didn't stop The Flash and Arrow bosses from having their own particular brand of fun with the episodes, either. Berlanti reveals that there are Easter eggs hidden in the crossover episodes that will pay off when Legends of Tomorrow debuts in January.

In addition to kick-starting Legends, part one of the crossover also dropped some huge revelations for both The Flash and Arrow's individual storylines. Oliver (Stephen Amell) discovered what viewers have known since season two: he might have a son in Central City. But producers say this won't be the DC Comics character Connor Hawke, who is Oliver's son in the comic books and eventually becomes the second Green Arrow.

"When we came up with the whole idea of it, we didn't want to be tied into a character like Connor, and not be able to have him be a part of the show if we made him so young," Kreisberg says. "To give us the leeway to still have Connor Hawke be a part of the universe, that was the biggest reason we made that decision."

Expect that storyline to advance in major ways in part two of the crossover, including how it will affect Oliver's relationship with Felicity (Emily Bett Rickards).

As for The Flash, viewers saw Harrison Wells (Tom Cavanagh) successfully create a serum to replicate the speed force, Velocity 6. As a result, Jay Garrick (Teddy Sears) momentarily got his powers back and used them to save Wells' life after Patty Spivot (Shantel VanSanten) shot him.

"If you're a fan of the comics, you know that a big part of the comics is Velocity 9, and today you met Velocity 6," Kreisberg says. "So it's safe to say that there will be a few more iterations of that formula. How it plays out and how it works and who uses it and the effects that would have, that's something you'll have to watch for."

But now that Jay got a taste of his old powers, will he stick to his guns of not wanting anything to do with the serum? "He's not jonesing for a fix or anything," Sears says. "He's aware of what potential Velocity 6 has on his life. But he's very clear that he doesn't want to go down that path. But like anyone who has seen the other side, there are haunting memories of what could be or what could have been."

One unexpected outcome of Wells' injury is that the animosity between Wells and Jay might actually dissipate. "Jay is still very dubious of Wells and the carnage that he's created on Earth 2," Sears says. "But there is a growing understanding and respect. These two will begin to work side-by-side as members of Team STAR Labs going forward. But it's not like they're not going to be buddies or great friends."

Part two of the crossover airs on Arrow on Wednesday at 8 p.m. on The CW.