No superhero is an island. Costumed characters teaming up -- or fighting amongst themselves -- is one of the most enduring recurring themes in the superhero genre, dating back to the Golden Age.

In the "Flash" half of this week's crossover between the DC Comics-based CW series, the two title characters fought -- thanks to some superpowered villainy. Tonight, they team-up during for "Arrow" installment, "The Brave and the Bold." The episodes mostly stand alone, but with continuing plot lines running between the two, and several characters appearing on each other's series. In "The Brave and the Bold," written by Marc Guggenheim & Grainne Godfree Schwartz with a story by Greg Berlanti & Andrew Kreisberg, Digger Harkness (Nick Tarabay, playing long-time comic book Flash rogue Captain Boomerang) targets Lyla (Audrey Marie Anderson) -- and The Flash (Grant Gustin), Caitlin (Danielle Panabaker) and Cisco (Carlos Valdes) head to Starling City to help out the Arrow team.

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With the second half of the crossover airing tonight and both shows heading to their respective midseason finales, CBR News spoke with both "Arrow" and "Flash" executive producer Andrew Kreisberg and "Arrow" executive producer Marc Guggenheim at a screening event in Los Angeles. Both are lifelong comic book fans and frequent comic book writers, and spoke about the inherent pleasure in getting to collide the "Flash" and "Arrow" worlds on screen, and what the future of such interactions might look like.

CBR News: Andrew, I'm curious to hear more about the timing of this crossover, as it's happening relatively early in the first season of "The Flash." It sounds like another example of what's been said by the "Flash" team in the past -- not wanting to hold back on things like this, and just going for it. Do you see these episodes as part of that philosophy?

Andrew Kreisberg: Yeah. Doing this was one of the reasons we were excited to do "The Flash" -- that we could be doing this with both shows. We just don't believe in waiting. We didn't want anyone to think we were doing it for any sort of cynical reason, so we're just doing it, whether anyone thought it was a good idea. It wasn't a ploy to grab ratings. We just felt like this could be one of the biggest, coolest, most fun things we can do. Amazingly, we seemed to have kind of pulled it off.

You're a comics fan and a frequent comic book writer, so superhero crossovers obviously have a meaning to you. What was it like for you to see these characters intermingling to this extent?

Kreisberg: It's why we named the second episode "The Brave and the Bold." It literally is that. And with all the great comic books when one of them got whammied and turned against each other and you had to see Superman and Batman fight -- even in "Dark Knight Returns," watching Superman and Batman fight. Part of the genesis of the first episode was, "How do we get them at each other's throats?" and watch speed versus archery.

Which is also a classic comic book dynamic, two heroes fighting before teaming up.

Kreisberg: Yes! We were saying, one of the best parts of the "Avengers" movie was the beginning, when they're all at each other's throats in the forest, so how can we create a situation where that happens?

As someone closely involved with both shows, how important was it going into this not to just do something cool and fun, but two episodes that had real stakes for both shows going forward?

Kreisberg: That was paramount; that's always what we do. As much as fun as it is to see them fighting, we really wanted Barry to go through a great emotional journey on his side of it, and Oliver to go through the same. I always think of the "gimmick" episodes that people do. They should have real stakes, and they should be important. We always talk a lot about Joss Whedon -- when he did "Hush" or "Once More with Feeling." They were the gimmick episodes of "Buffy," but at the same time, they were huge changes on them, and really advanced the story. That was very important to us, so you have all of those things happening in both of these episodes.

Looking towards the future -- these shows are interconnected and will remain so no matter what, but in terms of doing a clear-cut "crossover" like this, is that something you could see maybe doing once a season? Couple times? Or have you not gotten that far yet?

Kreisberg: Doing it this time nearly killed us, because we basically had to shoot two extra episodes in the same amount of time, and it really was a giant scheduling nightmare that was very difficult on both crews, both sets of casts and also for the writers. But at the same time, you look at the results, and we're so proud of these episodes. There's certainly an appetite to try and do something like this again. Hopefully we'll find the right story and the right time, and hopefully the fans are here for it, too.

CBR News: Marc, as an executive producer on "Arrow" but not on "Flash," how did you enjoy working on this crossover, getting to play with those toys?

Marc Guggenheim: I loved writing the Flash characters. They were so much fun. I thought I'd have a difficult time getting the voices, but they came to me immediately, particularly Cisco. They're so much fun to write, and I think they've been so vividly drawn on "Flash" that it was a piece of cake. I didn't struggle with their tone or their voice at all as a writer.

You're a huge comic book fan and a comic book writer, and a comic book crossover is one of the most deeply, sacredly held aspects of superhero comics -- what was it like getting to mix these shows together, and really embrace everything that means?

Guggenheim: Oh, my God. You have to understand, the 10-year-old boy in me is pinching himself. I still can't quite wrap my brain around the enormity of that. I grew up reading comics like "Marvel Two-in-One," "Marvel Team-Up," "Brave and the Bold" and "DC Comics Presents." I always loved those team-up books. Those are my favorites. I always liked seeing different characters connect with each other.

At the same time, on television, my favorite shows growing up were "Bionic Woman" and "Six Million Dollar Man," and my favorite episodes that they would do were the crossovers. The opportunity to do a superhero crossover on television -- it checks off so many fanboy boxes for me that I don't even know really how to process it all.

One thing that you were clear about at the start of "Arrow" season three was, now that "The Flash" existed as its own show, superpowers were going to be contained there and "Arrow" would return to more grounded territory. Was it fun to step outside of that for an episode, and indulge a little bit more in the fantastic?

Guggenheim: Yeah, it really was, actually. And I have to say, what's fun about episode 8 for "Arrow" is, it proved to me as a writer and a producer, "Hey, you know what?" You can do metahumans on "Arrow" without feeling like the show is changing its tone too much.

So we may see more of that?

Guggenheim: You may. It's something that we all sort of collectively realized: "Hey, the show can handle that." So that's kind of cool. I may have to amend my earlier comment from the beginning of the year, just because this kind of works!

"Arrow" episode "The Brave and the Bold," the second half of "The Flash"/"Arrow" crossover, airs 8 tonight on The CW.