Marc Guggenheim Teases ARROW's 100th Episode, Reveals How SUPERGIRL Arrives In The Arrowverse

The CW's superhero shows have come a long way since Arrow debuted in 2011. Five years later, audiences will now have a crossover that features Green Arrow, The Flash, Supergirl, and many other heroes (and villains) from Legends of Tomorrrow. 

With Supergirl's arrival on the network, it was believed that they would be crossing all four shows over, but Arrow executive producer Marc Guggenheim clarified with EW that it will only be three shows that are featured, with Cisco and Barry travelling to "Earth-CBS" to recruit Kara at the end of an episode of Supergirl. “Some people call it a four-way crossover because it involves four shows; my ulcer requires me to call it a three-part crossover,” Guggenheim said. “The story that’s being told has a beginning, middle, and end: a beginning in Flash, a middle in Arrow, and an end in Legends. But Supergirl is very much a part of the whole thing, so we are crossing over four shows — four shows in three parts.”

Many fans believed that the reality-altering events of Flashpoint would be the catalyst that brought Supergirl to the 'Arrowverse', but were disappointed when no such event transpired. According to Guggenheim, it seems like Supergirl will remain on a separate earth, with the characters using breach technology to allow her to cross paths with the other heroes. “Last year, Supergirl established that Flash was able to make his way to what I call Earth-CBS, and it stands to reason that, with the proper breach technology, the reverse can happen,” Guggenheim explained.

A fact that flew under the radar was that Arrow's part of the story will also be its 100th episode, something that Guggenheim says some fans were vocal about, as they didn't want it to diminish from the important milestone. “When the news broke that the 100th episode was also going to be the crossover episode, people were up and down my Twitter and Greg [Berlanti’s] Twitter I think, in this case, in a very positive way,” Guggenheim said. “People didn’t want to feel like the crossover was highjacking what should be a really seminal episode and a seminal moment for the show Arrow, which I think is wonderful. Greg came up with an idea that really does allow us to have our cake and eat it, too.”

Nevertheless, Guggenheim promised that the episode will take special care to pay tribute to Oliver, his story, and his supporting cast. “I haven’t seen the episode all cut together yet, but it has some incredibly iconic moments,” he said. “It is a love letter to the show, it draws on all previous 99 episodes pretty much. Everyone who we could have in the episode, from a scheduling point of view, is in the episode. Even the people who we couldn’t have, because of conflicting schedules, are represented. At the same time, you’ve got Flash and Supergirl; that’s an enormous amount of fun. Certainly the recruits also play a very large role, an important role, in the episode. I’m really excited about it.”