“It’s a superhero a-go-go!”

That’s how executive producer Andrew Kreisberg describes the December 1 and 2 crossover episodes of his CW shows, The Flash and Arrow. Bringing together Oliver Queen (Stephen Amell), Barry Allen (Grant Gustin) and their teams, as well as villainous Vandal Savage (Casper Crump) and winged warriors Hawkman (Falk Hentschel) and Hawkgirl (Ciara Reneé) of the upcoming spin-off, DC’s Legends of Tomorrow, the outings may feature the most DC Comics characters assembled on screen since Smallville's Justice Society event, and Kreisberg can’t wait for fans to see this blended posse in action. “It’s insane to have them all together.”

It was also an insane amount of effort for both productions. Even though they film across the lot from each other in Vancouver, there were scheduling logistics to be hammered out, multiple fight sequences to be choreographed and, of course, hours of coordination by the writing teams to master a plot that’s big enough for Central and Star Cities. What they've come up with is an action-packed origin story centered on The Flash’s Kendra (Reneé), who discovers that she is actually a fine feathered heroine after being targeted by immortal killer Savage. “This is a crazy, full-on ‘To Be Continued’ crossover,” continues Arrow EP Marc Guggenheim, noting that unlike last year’s crossover—basically two separate stories that involved each show—this one “really feels like a 2-hour movie [airing] over two nights.”

Along the way, we’ll also get some of that always-entertaining interplay between The Flash and Arrow players, some of whom are still not used to dealing with things that defy explanation. “It’s really funny watching Digg [David Ramsey],” laughs Kreisberg. “He is constantly blown away by the Flash’s abilities." In addition, Kreisberg teases that there will be "great Baricity moments—not that Felicity is going to leave Oliver for Barry, but scenes between Grant and Emily Bett Rickards are always magical. They have such great chemistry.”

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As for those online grumblings that the crossover is really just meant to lay pipe for Legends, the producers promise that isn’t the case. “These [episodes] have important stuff going on for the narratives of both The Flash and Arrow, ” offers Kriesberg, while Guggenheim all but warns us that the already established members of the Flarrow universe are in for some serious shaking up. “The final moments of The Flash have a pretty big jaw-dropper and we pick up those threads in Arrow,” he says. “Then we do some things with the characters from Arrow…that are pretty epic and major.”

For more on The Flash-Arrow crossover, pick up the "Power" issue of TV Guide Magazine, on sale next week!