Last year's "Arrow" and "The Flash" crossover was such a big success for both shows that they decided to do another this year. While last year's installment pitted one hero against the other before ultimately deciding to work together as a team, this year's crossover will see Oliver and Barry being more comfortable working with each other as they team up to save their respective cities from being taken over by the bad guys.

2014's 'Flash vs Arrow' and 'The Brave and the Bold' were structured in such a way that fans didn't need to see both episodes to appreciate the crossover, but this year, the crossover will be a more integrated story. "Arrow" star Stephen Amell told MTV News that if the episodes were aired back to back in one night, it would run like a "two-hour episode of television."

The crossovers will also take the heroes out of their comfort zones as they will be seen fighting most of their battles in the other hero's city.

"In fact, most of 'The Flash' episode takes place in Star City, and most of the 'Arrow' episode takes place in Central City," said Amell.

The actor also revealed that both episodes will share a common villain, and it looks like whoever the Big Bad could be will be a big threat to both the Arrow and the Flash.

The crossover will also launch "Legends of Tomorrow," and Amell said that the crossover does a brilliant job of combining all three shows in one television event.

"It was logistically challenging, but I think when they're finished, whenever that is, because there's little pieces here and there to grab," he said.

"The Flash" star Grant Gustin told MTV News that in one scene of the crossover, they had a scene that had nine superheroes in it.

"Nine people with either powers or supersuits," said Gustin. "It was an amazing thing to look at, to look out over the scene and see the world that has been built over the course of three plus years."

The "Arrow" and "The Flash" crossover episodes will air later in the season on The CW.