It seems impossible to imagine that when Oliver Queen shot his first arrow at a tennis ball back in 2012’s Arrow premiere, he was heading down a path that would eventually bring one of DC’s most defining, and complex, stories to the screen. Yet, eight seasons later, Stephen Amell’s Emerald Archer is leading the charge into a breathtaking five-hour television adaptation of Marv Wolfman and George Perez’s Multiverse-shattering Crisis on Infinite Earths.

The highly anticipated crossover, which kicks off on Sunday at 8 p.m. (7 p.m. CST) on The CW’s Supergirl, is the largest superhero crossover in the history of the network and of DCTV in general. Featuring characters from all six of The CW’s DC shows and appearances and cameos from a who’s who of past and present talent, it will redefine DC’s TV universe the same way it did its comic universe back in 1985.

“I don't think we ever really felt like the TV universe was too complex,” explains Consulting Producer Marc Guggenheim, the mastermind behind the crossover. “We've only got eight years of continuity and DC had fifty. But the way we all sort of looked at it was, it's an opportunity. If we want to fix something, it’s there. If we want to change something, it's there. If we want to set something up, it's there.”

While The CW’s “Crisis on Infinite Earths” crossover isn’t a direct retelling of the comic, fans will likely be surprised how much of the iconic storyline seems to have made it into the TV version, even if it isn’t always a direct translation.

“You'll see that there are elements from the comic that we're tipping our hats to,” Guggenheim continues. “Like the quantum towers (which show up in the Crisis premiere) are from the first couple of issues of the comic. We wanted to nod to those. The scene where Lois and Kal-El put Jonathan in the pod is a nod not just to the origin of Supergirl and Superman, but the moment in Crisis on Infinite Earths #1 where Alexander Luthor is placed in a pod and rocketed off to safety. And then there's a pretty big nod to the comics in the third hour.”

“Crisis on Infinite Earths” involves the casts of Arrow, The Flash, Supergirl, Batwoman, DC’s Legends of Tomorrow and, for the very first time, Black Lightning. While impressive, though, that’s arguably to be expected in a crossover using Crisis as its source material. What’s elevated “Crisis” well above past CW crossovers, and excited DC fans beyond the ones who watch the CW shows, are the guest appearances and cameos by actors and characters from other DCTV and movie projects. The crossover features plenty of them, including Brandon Routh’s return to the role of Superman, Tom Welling’s Smallville Clark Kent and Batman: The Animated Series’ Kevin Conroy as an aging Bruce Wayne, who has a surprisingly charged scene opposite Batwoman’s Kate Kane.

“Kate getting to meet Bruce Wayne or a version of Bruce Wayne is something obviously we've dreamed about doing, and so to be able to find a way to do it felt like such a treat,” reveals Batwoman showrunner, Caroline Dries. “She’s coming face to face with this guy who's already been there, done that, and she's just starting off. It felt really poignant for this chapter in her life to come up against him.”

Adds DC’s Legends of Tomorrow co-showrunner Keto Shimizu, “I’m just one of Kevin Conroy’s biggest fans. He's my favorite Batman and I've been obsessed with Batman my whole life. So, just hearing that voice and seeing him get to play it, it's really amazing to watch.”

While Conroy’s involvement in “Crisis” has been previously announced, fans may be surprised at some of the secrets that the crossover writers and producers have managed to keep under their hats (let’s just say you won’t want to tune-in late to Sunday’s episode). But for the writers behind the event, the heart and soul of the story are the frequently high-stakes choices characters are asked to make and the emotional fallout from them.

“It needed to feel emotionally significant for everybody,” says Shimizu. “Yes, you can have all these incredible cameos from all these fun, different versions of DC characters that we know and love so much, but at the core of it, we really wanted to keep track of the main characters from all of our shows and have them go through something really incredibly significant for their characters in ‘Crisis.’ And I think that honestly is what grounds it and makes this ‘Crisis’ important. On a very deep level, you feel for these characters as they're going through this amazing adventure together. It brings them all closer together, which I think is the definition of epic in terms of the relationship that all these shows have with one another.”

“One of the things we took a lot of pride in was being able to write an interaction on Argo City that kind of reimagines Zor-El saying goodbye to Kal-El,” shares Supergirl showrunner Robert Rovner. “Also, there's a scene you get between Mia and Oliver that I quite love when he gives her an Arrow costume, and there's a lovely scene between Clark and Kara on the balcony when they're talking about legacies and how do they move on from the destruction of Argo City at the beginning of the hour.”

None of which is to say that “Crisis on Infinite Earths” is only going to matter to you if you already follow the Arrowverse. While some of the shows, notably Arrow and The Flash, have been seeding the crossover in the episodes leading up to it, “Crisis” itself is a lot of fun even if you’ve never watched the shows involved.

“You don't need any sort of setup,” promises Guggenheim. “I mean, it's fun to see last year's crossover and know that a Crisis is coming and that Oliver made this bargain with the Monitor, but you get all that information in the body of the story.”

However, if you are a fan of the shows, know that “Crisis,” unlike some of the past CW crossovers, will have lasting repercussions on all the shows involved.

“It really resets a lot of what's happening on Supergirl for the second half of the season,” Rovner shares. “That was another thing that was challenging about this crossover that's different from the others. It really is a huge event, and it impacts everything happening on the show.”

“During the Crisis, Barry will do something that is very significant that will have ramifications for the remainder of season six of Flash,” reveals Guggenheim.

“It sets up our season (on DC’s Legends of Tomorrow), both the mythology and Sara Lance's sort of trajectory coming out of this,” explains Shimizu. “This hits her pretty hard in a good way.”

But perhaps no show is impacted more than the one that started it all. Arrow is now in its final season—a shortened season of only ten episodes. There are two of them remaining after “Crisis,” and the content of those two hours remains a pretty big mystery. But it’s clear that they’ll be considerably different than the ones that came before the event.

“We’re going towards the end of our season and series, so it’s different than the crossovers have been in the past,” shares Arrow showrunner Beth Schwartz. “It changes literally everything on Arrow.”

The five-part "Crisis on Infinite Earths" crossover event kicks off on Sunday at 8/7c on Supergirl before continuing on Monday at 8/7c on Batwoman and Tuesday at 8/7c on The Flash. The final two parts will air in January on Arrow and DC's Legends of Tomorrow.