A question has existed since the dawn of superheroes: Who would win in a fight? Batman or Superman? Iron Man or Captain America? Brains or brawn? On Dec. 2 and Dec. 3, The CW will pose that query with the heroes of two of the network’s most popular series, “Arrow” and its super-powered spinoff “The Flash,” in a two-night crossover event. In the Dec. 2 “Flash” installment, tellingly titled “Flash vs. Arrow,” Emerald Archer Oliver Queen (Stephen Amell) goes head to head with Scarlet Speedster Barry Allen (Grant Gustin), after a Central City meta-human manipulates Barry’s emotions and sets him on a very destructive course.

Variety spoke to the stars and executive producers of both series at a recent screening for the crossover, and while both hours are self-contained enough to appeal to new viewers, the event should be catnip for fans of the shows and the DC Comics properties on which they’re based. Here’s what we learned about “Flash vs. Arrow”:

The fun is contagious…
“One of the more fascinating things about the crossover is that the tone of each series affects the characters that are coming into it,” previewed “Flash” star Carlos Valdes (Cisco).

“Arrow’s” David Ramsey (Diggle) agreed, “‘Arrow’ in general is dark and brooding, and ‘Flash’ is light and fun, so naturally when you get these two worlds together, you’re gonna have built-in comedy. The writers don’t shy away from that — Diggle is a complete and total fish out of water; he’s the ex-Army Ranger that does everything by the book, so when he meets up with these people in Central City, he is completely and totally flabbergasted, so we play the comedy of that.”

…But the stakes are real
While the “Flash” episode is undoubtedly the lighter of the two, it’s not all fun and games; both teams have a lot to learn from each other — not just in terms of how they deal with the obstacles they encounter on their missions, but also about what it means to be a hero, in every sense of the word.

“I think Team Arrow in Central City learns a couple of important lessons about what exists out there in the world,” Amell noted, although the producers maintain that Starling City won’t suddenly become a hotbed of meta-human activity now that they’ve been exposed to “The Flash’s” super-powered foes.

Executive producer Andrew Kreisberg promised that both episodes would propel their respective series’ story arcs forward, even if the overarching mythologies of the two shows take a backseat for the week: “There’s definitely a big surprise for Oliver — although Oliver isn’t fully aware of it — that happens on the ‘Flash’ side of things, that is going to have major repercussions on ‘Arrow’ down the road. I think Barry grows up a lot in this episode, which is nice. It was important for both Barry to have a real journey and Oliver to have a real journey. I think Barry has been coasting along on the speed and his powers, and he doesn’t always think things through and that’s bitten him on the ass, and Oliver calls him out on it. But by the same token, Oliver has chosen to let go of Oliver Queen this year and be much more The Arrow, and Barry is there to remind him that Oliver can also be a person. It was important that both shows shined and both shows demonstrated their strengths, and that even though we joke it’s Flash vs. Arrow, there really is an equality, not necessarily of skill but certainly of heart.”

The episodes will provide a steep learning curve for Barry, who has to suffer some tough love from Oliver in “Flash vs. Arrow.” But Gustin admitted that what doesn’t kill Barry (like being shot with Oliver’s arrows, for example) will certainly make him stronger in the long run: “With every episode, Barry trusts his team a little bit more, and at the same time, he’s had some questions with what’s going on with Harrison Wells [Tom Cavanagh]. He doesn’t think anything major, but there’s been some distance and some weirdness at times that we’ll all start questioning. But [after the crossover], Barry has more confidence and feels like he’s on more of an even playing field with Oliver, who he’s always looked up to and had on this pedestal. I think Barry thinks he can hold his own now in this world of meta-humans and this city he now needs to protect. He’s accepted the role at this point.”

Oliver has met his share of manipulative authority figures over the course of “Arrow’s” run so far, but Amell played coy when asked if his character would be able to sense something amiss with Dr. Wells that perhaps the “Flash” team is too close to notice. “That’s one of my favorite parts of the crossover, the interaction between Dr. Wells and Oliver,” he teased. “Less their interaction, and more Oliver’s reaction to it.”

There’s no time for romance
While Barry and Felicity (Emily Bett Rickards) seem perfect for each other on paper, they’re currently too hung up on other people to explore their obvious chemistry, and after Felicity’s last sojourn to Central City, the two are firmly back in the friend zone, according to Gustin.

“Nobody’s crossing any boundaries at that point, they’re both sticking to what they said they were going to do and are just friends for now, and that’s all it can be,” he admitted. “It never really even comes up, because we’re focused on so many other things during those two episodes, and I actually never found myself thinking it was strange that it was never addressed because of how much happens in those two episodes — it feels right that it’s not something that we even deal with.”

That’s not to say there aren’t plenty of lingering looks between Barry and Iris (Candice Patton), and Oliver and Felicity, over the course of the crossover. But if you’re hoping that Felicity’s kiss with Ray Palmer (Brandon Routh) will be discussed, you’re out of luck — although executive producer Marc Guggenheim promised that developments are coming on that front in an upcoming installment of “Arrow.”

“We’re going to be exploring the ramifications of that kiss in the [Dec. 10] midseason finale,” he teased, promising that comic book fans who know Ray Palmer’s secret identity won’t be disappointed. “We finally revealed the Atom armor, and that’s going to develop further. Who knows, maybe Felicity might find herself drawn in to what Ray has up his sleeve.”

While the kiss was clearly not unwanted, Rickards pointed out that Ray “sorta kinda walked away, so they need to reach an understanding with their work relationship, with where they stand now. Ray is an adult, so he’s gonna step up to the plate — he’s a nice dude, and he has respect for Felicity.”

Oliver obviously wasn’t thrilled to see Felicity locking lips with the man who took over his company, but Amell admitted that Oliver doesn’t see Ray as a rival: “He came in, he gave a better pitch to the board of Queen Consolidated, now Palmer Technologies, and the fact that he kissed Felicity… it bothers Oliver, but that’s Oliver’s issue, that’s not an issue with Ray. I think that eventually they’ll be at odds later in the season, but that’s a ways off.”

There’s no I in team (but there is in Oliver)
Rickards previewed that one of the biggest challenges for the two teams in the first part of the crossover is learning how to coexist, when both groups evidently have their own methods of working a case. “It’s [about] Felicity’s problem-solving game with personalities; she’s got to read how she’s going to get these personalities to work together, and she’s becoming more of a trained psychologist every day, in a sense. And they need each other, and that is definitely understood on all levels from everyone… but there’s a little bit of an ego there, a little bit of a brawn thing, a little bit of a misunderstanding and then there’s the necessity.”

“Flash” star Danielle Panabaker agreed, “Team Arrow are used to doing exactly what Oliver says all the time as he says it; Team Flash is a little more of a team, we’re all working to help Barry. Obviously he’s the one making the final decisions, but it is a bit more of a team effort and Oliver’s certainly not used to that, and not open to it either.” But just because The Arrow is kind of a big deal in vigilante circles, don’t expect Team Flash to be too star-struck. “Caitlin is very protective, because she thinks Barry’s a big deal and she thinks Flash is a big deal, so she’s not necessarily swayed by [The Arrow].”

“The Flash” airs Tuesdays at 8 p.m. and “Arrow” airs Wednesdays at 8 p.m. on The CW.