4) Konstantin Kovar
Season 5 of Arrow is the last year the series will feature flashbacks building up to Oliver Queen’s return to Star City, and Konstantin Kovar has been a big part of that. As of right now, we have no idea how his story will end, but the hero is out for revenge and to take him down, so things ending with his apparent demise at the hands of The Hood seem likely. However, we are talking about a world based on comic books here, so him surviving and returning to Star City is definitely feasible.
Of course, that begs the question of why he hasn’t just made it his mission to take down Oliver? Seeing as Vigilante has targeted both him and the Green Arrow on multiple occasions though, there’s a strong chance Kovar is biding his time and has something greater up his sleeve. What that could be may very well end up being a huge part of Arrow‘s upcoming sixth season, and we’ll obviously know whether or not this theory is accurate once the show’s current run wraps up.