<Li> Cynthia Addai - Robinson as Amanda Waller </Li> <Li> Nick E. Tarabay as Digger Harkness / Captain Boomerang </Li> <P> The first indication of potential crossover events in the Arrowverse occurred on The CW during the 2013--14 television season, when Barry Allen was introduced in the eighth episode of Arrow's second season ahead of the debut of The Flash . In July 2014, it was announced that the eighth episodes of the third season of Arrow and the first season of The Flash would be a two - hour crossover event . The crossover was originally planned as the seventh episodes of each series, but was pushed back due to the large amount of work needed to accomplish it . In particular, the schedule coordination of trying to "jam another episode into the 23 - episode schedule for each of (the) shows ." Marc Guggenheim, creator and executive producer on Arrow, explained that there was "no financially responsible" way of executing the crossover, with budgets being blown, long hours and the actors having to film scenes from both series on the same day . </P> <P> Andrew Kreisberg, creator and executive producer on both series, said, "It's really going to be an adventure with the Arrow and Flash on both episodes . Watching the two teams come together and fight alongside each other, it's one of the most fun parts,...we just don't believe in waiting . We really believe in accelerated storytelling ." Kreisberg explained that since they are all comic book fans themselves, they have all debated the age - old question of which superhero would win in a fight; "So, the idea that (the Flash and Arrow) would fight each other in one of these episodes was one of our earliest ideas, and that the cast members would have that Comic - Con argument on camera was one of our earliest ideas ." Greg Berlanti, creator and executive producer on both series, explained that "crossovers are part of (the characters') DNA,...and if we waited..., then we would be depriving the audience of something we all wanted to see". </P>

When does the flash first appear on arrow