Greg Berlanti is executive producing multiple series including Arrow, The Flash, Supergirl, The Mysteries Of Laura and I may be forgetting one or two. Andrew Kreisberg and Marc Guggenheim are both involved in Arrow, The Flash and the spinoff series (I knew I forgot one) and Kreisberg is part of Supergirl as well. Oh, and there's the Vixen cartoon too. There are only so many hours in a day so it was obvious that help needed to come from somewhere.
Guggenheim announced yesterday via twitter that Wendy Mericle will be stepping up as co-showrunner for Arrow next season. Mericle has written or co-written 13 episodes of Arrow so far including this week's The Fallen. Previously she has worked on Desperate Housewives, Eli Stone and Smallville.
— Marc Guggenheim (@mguggenheim) April 23, 2015
Arrow airs Wednesday at 8 PM on the CW.