Finally, a new trailer for "Legends of Tomorrow" was unveiled last Monday and it gave a glimpse on how action-packed the crossover TV series will be.

Here's the trailer. As fans can see, the heroes will go back and forth in time to prevent Vandal Savage from bringing catastrophe to the world. Also, each character will have their past shown like how Captain Cold will see his young self. Also, Firestorm will be donning a new costume that is much appropriate to the comics. More importantly, Rip Hunter made a reference to Batman and Superman, will they have their own shows in the future?

Nevertheless, "Legends of Tomorrow" won't be airing until January 21 but The CW have prepared perhaps the best prelude to the show with "The Flash" and "Arrow" crossover airing on Dec. 1 and 2, respectively.

The main stars of the show, Stephen Amell and Grant Gustin spoke about the two-part crossover and for Amell, this is the biggest achievement so far for both superhero shows.

"These two crossover episodes standing together will probably be, in my mind, the pinnacle achievement for both shows," Amell said via MStarz.

He also said that fans can expect a lot from this two-hour special as it will have a better continuity compared to last year's crossover.

"Most of the Flash episode takes place in Star City, and most of the Arrow episode takes place in Central City," Amell said. "We have a common villain, which was not the case last year. And, just in general, we've done an excellent job of weaving not just two shows, but three shows together."

Gustin, meanwhile, is just thrilled to have more people climb on board as it adds to the excitement and hype heading into Legends.

"It feels even bigger," Gustin added. "I feel like more people are a part of it this year from both sides, and we're tying in Legends, obviously, so it's just bigger."