Amell mentioned at Fan Expo Canada this weekend that not only does he expect Oliver Queen to appear in all three shows, but there will also be an Arrow character who will be traveling between Arrow, The Flash and this spinoff. Here’s what Amell said, according to Comicbook.com:
I know that there’s a plan for one character who originated on Arrow and is not one of the main characters on the new spinoff to sort of hover between all three shows and that will be their job, so to speak. So you’ll see a lot of interconnectivity next year.
There are several candidates that would fit this description. With A.R.G.U.S.’s global presence, maybe Amanda Waller will step outside of Arrow’s confines and pop up in The Flash early in its second season before appearing in the spinoff. Her shady work has her dealing with both crimefighters and criminals, so if there’s anybody that could get superheroes and supervillains to work together – and by “get” I mean “probably blackmail” – it would be her.
There’s also the chance it could be another villain. Perhaps Captain Boomerang, a noted Flash adversary who debuted in the Arrow episode “Draw Back Your Bow.” However, my main guess for this mystery character is the spectacled IT expert Felicity Smoak.
Since her debut in the Season 1 episode “Lone Gunmen,” Felicity has grown to be one of Team Arrow‘s cantral members and one of Oliver’s main love interests. She is also the core thread of connectivity between Arrow and The Flash, having struck up a friendship/pseudo-romantic interest in Barry Allen. She appeared in The Flash episode “Going Rogue” to help the S.T.A.R. Labs team stop Captain Cold, returned later with Oliver and Diggle in the episode “Flash vs. Arrow” to track down Captain Boomerang, and will revisit her Central City friends with her boyfriend Ray Palmer in next week’s episode “All-Star Team-Up” to get some help with the A.T.O.M. suit. With her semi-frequent travels between Arrow and The Flash already set, and Ray being one of the spinoff’s main characters, it’s not hard to picture Felicity as the connective tissue.
Whomever this Arrow character ends up being, he or she will be joining a cast that consists of Brandon Routh as Ray Palmer/The Atom, Victor Garber as Dr. Martin Stein, Caity Lotz as an unconfirmed character, Wentworth Miller as Captain Cold, Dominic Purcell as Heat Wave, Ciara Renée as Kendra Saunders/Hawkgirl and Arthur Darvill as Rip Hunter. Two other spinoff characters that haven’t been identified yet include a “Mystery Hero” and a big DC villain who hasn’t been used yet.