Felicity Smoak pegged it exactly right. The CW's ambitious four-part crossover – spanning over "Supergirl," "The Flash," "Arrow" and "DC's Legends of Tomorrow" – is the best superhero team up ever. The collective heroes must assemble to defend the Earth from alien invaders knows as the mind-controlling Dominators. It's heroes versus aliens – and the viewers are the winners.

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"Arrow" fight choreographer James Bamford switched hats and made his directorial debut with last season's episode, "Brotherhood." He subsequently stepped behind the camera for a number of "Arrow" episodes, including the third instalment of the crossover, "Invasion."

Bamford recently spoke with CBR about the challenges of orchestrating such an epic event, the scope and scale of the production and how the Arrow's 100th episode pays off for the show's fans. An looking beyond the Dominators' creepy agenda, Bamford discussed his show's take on the villainous Prometheus and the coming of Talia al Ghul.

CBR: What was your reaction when you received the script for "Invasion!?"

James Bamford: How are we going to pull this off in eight days? To be honest, my reaction was it really speaks to the character base, the heart of the show and the ties that bind, if you will. I was really touched.

There's a lot going on in this episode. What were some of your concerns when it came to pre-production?

Without giving anything away, there were location concerns. There were the usual concerns we encounter on every episode. We're always racing against time and budget. It's a very ambitious episode. As you know, it has elements to it that we don't usually address on the show, so how do we deal with those in our world? How do we make this about the 100th episode of Arrow and give it the biggest nod possible, and give it the time and care it deserves for the fans? It's a big responsibility, so we wanted to make sure we got there and I really think we did.

Team Arrow and the newbies are a handful already. How difficult was it juggling heroes from four different series and giving them all space to shine?

It was no problem [Laughter]. Our schedule was spread in such a way that I wasn't inundated with giant days of 10 or 12 cast members in my scenes. I was fortunate enough to have my larger scenes spread out, which made it much more manageable. We were shooting all the crossovers essentially simultaneously. Some days some of our actors would have to start the day on "The Flash," they would get in a shuttle and come over to "Arrow" and then we'd send them over to "Legends." It was insane.

I was very fortunate to have jumped in on a "Supergirl" episode and work with Melissa [Benoist] a few weeks prior to initiating the crossover event episode. I had some experience working with her over there, and I've worked with Grant Gustin, Brandon Routh and Caity Lotz before. It was just like, "Come on over guys." It was like a big party.

Every "Arrow" episode culminates with a big brawl. What can you tease about how things blow up in "Invasion?"

I can tell you that's generally an act-five challenge in the script. The act five of the script extends into act six and then morphs into something else. The biggest challenge for the act-five sequence would have been the weather, the storm that we encountered. We weren't alone. I believe one or two of the other shows – "Flash" and possibly "Legends" – also encountered the same challenges. A big rain storm came through Vancouver and really did a number on anybody who happened to be filming outdoors those days. Everybody came together, pushed through and toughed it out. I'm really proud of what we got out of that.

Are the aliens all CGI creations, or did you go practical in some cases?

They are real aliens. We did a big casting call in the universe. David Rapaport has contacts on Saturn and Mars and a few of the other planets. Quite a few different aliens showed up. It came down to what origin of planet fit into our universe. That was one of the first questions they asked them. "Which planet are you from?" It was a big casting search. I can't give away any secrets.

There's never been a network crossover like this before. What was your sense of the scope and scale while filming?

The "Arrow" crossover, because of being the 100th episode, tried to keep the storylines and the concept within the Arrow universe, and within the wheelhouse of the fanbase, in an original and interesting way. Greg Berlanti put a lot of thought in how to go about this and honor the fact that it's "Arrow's" 100th episode and not just part of the crossover event. I think when you see this, which will be the third night as the crossover starts on "Supergirl," you'll see that it takes a different twist from the other crossover episodes.

You directed "Arrow's" first two episodes this season and now "Invasion!" How many more are you hoping to squeeze in?

That's it for the season. The rest of the season is booked. It's pretty much usually booked at the beginning of the year. We have a bunch of new directors. Not new, per se, to the business, but new to the show. They bring with them different talents and viewpoints. I'm looking forward to working with all of them.

In the show, we've tried to recapture certain aspects of Season One and the grit. It was really nice to be able to start off the season and set the tone and somewhat reinvent – or bring back – the original Arrowesque feel. I'm here to help the other directors in following through with the intent coming into this season. Of course, I'd love to do more episodes, but you can't do everything.

There's another big threat looming after Arrow deals with these extraterrestrials. How are you approaching Prometheus compared to Oliver?

There's a duality happening with Prometheus' origin in a way with Oliver. Oliver and Prometheus are basically a yin and yang, if you will. Two sides of a coin. I can't really go into the approach of the character without giving too much away.

How do Prometheus and Oliver differ in terms of their fighting styles?

Prometheus is trained internationally. He has a huge repertoire of different skills and weaponry and, of course, hand-to-hand combat. We took one of our performers in the Prometheus wardrobe and experimented with different movement types and what was more intimidating. We combined different martial artist skills, once again depending on what was required for the moment as opposed to sticking to one style. Especially when they are "masters," I don't like them to rely on one particular skill or be boxed in.

Finally, another new player is Talia al Ghul. How excited are you to tackle Talia and her mythology, which has been layered in over the seasons?

I'm very excited. We are big fans of Nyssa and Katrina Law, who is absolutely wonderful and just a joy to have around, as well as being remarkably talented. Then there's Lexa Doig. She's just fitting right in. I think she'll be bringing something to the role you haven't seen before. She has a quality of her own. You'll be interested in how we've woven Talia into our mythology. She definitely makes an impression on Oliver Queen.

Starring Stephen Amell as the Emerald Archer, "Arrow" airs Wednesdays at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more.