<Tr> <Td_colspan="2"> List of Arrow episodes </Td> </Tr> <Tr> <Th> Followed by </Th> <Td> "Heroes Join Forces" </Td> </Tr> <P> "Flash vs. Arrow" is the first annual Arrowverse crossover event, broadcast on The CW, featuring episodes of the Arrowverse television series The Flash and Arrow . The event began on December 2, 2014, with The Flash episode "Flash vs. Arrow" and concluded the next day with the Arrow episode "The Brave and The Bold". The crossover sees Team Flash (Barry Allen / Flash, Caitlin Snow, and Cisco Ramon) helping Team Arrow (Oliver Queen / Arrow, Felicity Smoak, and John Diggle) take on the boomerang - wielding villain Captain Boomerang, while Team Arrow helps Team Flash confront the metahuman Roy Bivolo . </P> <P> A crossover between the two series was announced in July 2014, after Barry Allen had been introduced in Arrow's second season ahead of the debut of The Flash . By the following September, the scripts for each episode had been written, with filming occurring shortly before the end of the month and into October 2014 . The crossover sees every main cast member of each series who appear at least in their own series, with additional actors and characters also reprising their Arrowverse roles . </P>

When do the arrow and the flash crossover