Arrow, Flash, Supergirl, Legends Actors Tease Invasion Crossover

On Saturday, at EW PopFest, Melissa Benoist, Stephen Amell, Grant Gustin, Caity Lotz, and super-producer Greg Berlanti debated which hero would win in a fight and teased The Flash-Arrow-Supergirl-Legends of Tomorrow crossover event — featuring characters from all four shows joining forces when The Dominators, an evil and technologically advanced alien race, invades Earth-1.

"It was really cool," Amell began. "We had our individual scenes, but then we had scenes where there were like 20 superheroes there in this big airplane hangar. And it looked like and felt like — and I think the fans will feel like — this is a big 3-4 hour movie that we are putting on."

Even though Supergirl and The Flash had a one-episode crossover last season, this is Kara's first time meeting the rest of the characters from the Arrow-verse. How will she react to them? "I think Kara just wanted to be accepted and be like a part of the cool kids," Benoist offered. "And I felt the same way. It was so fun to be in this big group setting where everyone... It was like this infectious environment where we all.. It felt really cool. But she had good interactions with almost everyone there."

Crossovers are nothing new for Gustin, but this one feels different than the previous ones. "It's just a lot bigger," Gustin said. "Last year was Flash and Arrow and now... We have 17 characters in multiple scenes and almost everyone interacts with every other character, at a certain points. So, it's huge! Huge."

Berlanti shared how the crossover will begin, seeing as though Supergirl is on another Earth. "They all have their own continuing storylines thoughout it," he explained. "But it really does feel like in the middle of the whole season a 3-hour movie. It starts a little at the tail-end of Supergirl, because she's in a whole other universe, on a whole other planet, so having to go get her. And then it really begins on the night of The Flash. It's three parts and called 'Invasion.' The complex they talked about shooting in: We found an exterior shot that looks a lot like the Hall of Justice, so we like that."

Supergirl airs on Mondays at 8 p.m.; The Flash on Tuesdays at the same time, Arrow on Wednesdays, and DC's Legends of Tomorrow on Thursdays.