With Arrow being renewed for a sixth season there are numerous storylines I think they could adapt from the comics or bring back from the show.
Anatoly becomes KGBeastAfter the episode "Bratva" it's clear there are some tensions between Oliver and Anatoly and I'm starting to think they might have Anatoly embrace his villainous alter-ego KGBeast, and become the main antagonist of season 6. I actually thought this a while ago when Oliver forced Alexi Leonov to find Slade and Slade killed him that Anatoly might be pissed about that. Now 3 years later I was proven right even thought Anatoly later admitted to never liking Leonov. He also told Oliver that oaths are for life including his oath to the Bratva so Oliver's continued dismissal of this, might cost him when Anatoly comes asking for another favor if his interests bring him to Star City. I really don't want this to happen but I didn't want Slade to become Deathstroke either and look how that worked out. Now that Oliver has recently demonstrated a willingness to aid the Bratva if it means protecting his friends and family, perhapes Anatoly will force Oliver to maintain his oath or face consequences. Wheather he'd be a cyborg-like character like in the comics or simply a mob boss commanding his underlings I don't know, but either way I'm convinced he's starting to embrace his villianous alter-ego. After all Arrow was only meant to run for 5 seasons and now it's going further so they're gonna have to start branching out with their villains.
Green Arrow and Deathstroke rematch/team-upThis one is without question. Deathstroke is still the most forbidible foe Green Arrow has had to date because of all the torment he afflicted upon him while Oliver was basically helpless to stop him, and because of his personal connection with him. I still consider him his true archenemy. While other foes such as Ra's al Ghul and Damien Darhk were physically more powerful than Slade, he still remains Arrow's best villain because of the aforementioned factors, although I do admit Prometheus is starting to rival Deathstroke in terms of that title. That said Deathstorke is in serious need of a come back so we can see a rematch between him and Green Arrow but to spice it up, they should be forced into a reluctant team up against a common enemy, maybe some enemy holding Slade's son Grant hostage who even he can't defeat alone, allowing us to see them working together again just like in Season 1. While Slade will probably never forgive Oliver for what happened to Shado a reluctant team up may allow Slade a chance to escape, and wont' actively seek out Oliver provided he does the same. This could also allow Deathstroke to recur in the other shows. I am also aware that Deathstroke is going to be in the Batman movie coming up but still the fact that Deathstroke and Deadshot have both appeared as hallucinations this season, doesn't mean they aren't willing to bend the rules. Also KGBeast himself was in Batman vs Superman and yet he is still in Arrow.
Black Siren redemptionI have made several posts about this and despite the appearance of Dinah Drake I have not given up hope on this idea. I still think an Earth-2 Laurel reform story has the potential to be one of Arrow's best written storylines, if they do it right. Many people seem to think that since she didn't reform in the Arrow episode she was in recently, that means she won't at all but come on guys. If she is going to reform did you really think it would take just one episode? Earth-2 Laurel has been a criminal since 2013 so chances are she's convinced she can't be anything else, so if Oliver is going to talk sense into her chances are it will take more than a few tries, and probably a few fights. I am aware that Earth-2 Laurel has killed more than a few people and is without question insane from having lost Earth-2 Oliver, and probably the rest of her family, but I still think Oliver could convince her to channel her sociopathic tendencies on those who deserve it and becomes more of an anti-hero than a full villain. Remember she is Laurel's doppelganger and she was selfless and courageous so I'm willing to bet Earth-2 Laurel still has some of these traits buried deep down somewhere. After all Mick Rory loves to burn things, people included, and did so to a lot of people and now he's a time travelling hero. An Earth-2 Laurel redemption story could also be good story material for Quentin who is barely coping with losing Earth-1 Laurel and is then forced to interact with her doppelganger. I think if Quentin helps her find her sanity again it could be a way for Quentin to find closure with losing Earth-1 Laurel, if he and Earth-2 Laurel form a surrogate father/daughter bond.
Arsenal x CheshireThis is one comic storyline I would love to see if Roy ever comes back to the show. Jade Nguyen / Cheshire is a League of Assassins trained mercenary who encounters Roy Harper, and the two fall deeply in love despite Roy being a hero and Jade being a villain. One encounter between them results in a daughter named Lian Harper who Roy raises while Jade continues to be an assassin. I think this story is very much adaptable and I think they may have made a hint towards it already. Back in 1x22 when Thea is trying to talk Roy out of searching for The Hood using Oliver as an example of someone she lost he replies "I lost someone too, and they aren't coming back!" but didn't go into detail. Maybe Roy and Jade met when they were teenagers and fell in love but somehow Roy came to believe her dead, only for her to turn up alive later. It would also be fun to see Thea having to fight her ex-boyfriend's ex-girlfriend. They could also adapt the Lian Harper story by revealing that Jade was pregnant prior to her vanishing and Lian now lives in foster care, and Roy would obviously want to be involved in his daughter's life.
Vandal Savage and Roy Harper's relationWhile we're on the subject of Roy I think they should bring his relation to Vandal Savage into it. In the comics Savage is actually Roy's ancestor as he fathered a child with an unknown person who started a bloodline, which eventually led to Roy's conception. It would be good story for Roy if he returned but was then confronted by a revived Vandal Savage trying to tempt him in joining his side, making Roy realize he is the descendent of the next Hitler. I don't think Vandal Savage is done on the Arrowverse, as Malcolm Merlyn still has the ashes of his 2016 self somewhere and we know that version of him will be restored to conquer the world in 2166. I actually think we might see him at the end of Legends Season 2 as Malcolm is antagonising them as part of the Legion of Doom, so he may restore Savage as some kind of twisted ploy against the Legends.
Given how often they've introduced Batman characters I'm surprised they haven't introduced Nightwing, given the amount of Bludhaven references they made, and we even briefly saw it in Arrow 1x16 with the bar Deadshot and China White met in. Green Arrow has always been based more off Batman than the traditional Green Arrow so it be funny to introduce Nightwing the same as he is in the comics, a muh cockier and laid back yet still just as determined version of Green Arrow. This could also implicate the existance of Batman in the Arrowverse if he mentions to Green Arrow having a tutor that's "just like him", that would be hallariously awesome.
Hal Jordan / Green LanternPeople have been begging for this for years and why not? Introducing Green Lantern could be the most amazing thing this show has ever done. There have already been sublte hints towards a Green Lantern appearance including the brief appearance of a pilot named "Jordan", in Arrow 4x01 in the flashbacks, and in The Flash 1x22 when Barry explains to Captain Cold that Ferris Air was shutdown because "one of their test pilots dissaprared". I thought maybe they wouldn't because introducing Hal would mean including aliens but since we've now seen the Dominators, and Supergirl now exists in the Arrowverse via Earth-38, so there really is nothing holding them back from this anymore. I am also pretty sure that Todd Rice/Obsidian in Legends is, as per his comic counterpart, meant to be the son of the first Green Lantern, Alan Scott. I am aware of the Diggle is Green Lantern rumors but considering he's now Spartan, I don't really buy into this but hey I could be proven wrong yet. Either way a Green Lantern would be awesome.
John Diggle and Connor Hawke meetingThis may be more of a Legends of Tomorrow based story but since it involves one of Arrow's main characters it could be done in Arrow. We were introduced to John Diggle's future son John Diggle Jr aka Connor Hawke in LOT 1x06 in a potential future. I think it would be awesome if Connor somehow ended up in the present day and had a team up with his father and gave us a Green Arrow of two times team up with both Green Arrows at their prime. I would also like to see Diggle's reaction to knowing that his son will be his best friend's successor, and perhapes Diggle's knowlege of the future his son is going to grow up in may allow him to prevent it. I would also like to see where John Jr gets the name "Connor Hawke" from in the first place.
Malcolm Merlyn's deathAs much as I love Malcolm Merlyn there is no question that he needs to go eventually, and I call for the show's last season, in some epic final showdown between him and Oliver. However I don't think Oliver should be the one to kill him as he is Thea's father, so that said I think during this Green Arrow and Dark Archer showdown, he should be killed by Speedy forced to choose between her father and her brother as that's always been a recuring storyline of hers. While Thea and Malcolm aren't on the best of terms and have never really been, Malcolm is still her father and it will still bother her that she killed her own father. In this way Malcolm will still have kinda won as Thea will have become a killer by choosing to save someone she loved which is what Malcolm has been trying to prove to her for some time now.
More ConstantineJohn Constantine's introduction was one the best parts of a crappy fourth season and it allowed us to see the beloved character again after the series was wrongfully cancelled, and with the upcoming animated web series, we could very well see occasional guest appearances in Arrow. Remember Oliver does owe John a favor for restore Sara's soul so there is room for him to come back, maybe aiding him in one of his relic hunts as Oliver still has the anti Damien Darhk magic tattoo thing which Esrin Fortuna mentioned does many things. I also found Thea's comment about John very funny, "He's a spcific kinda yummy", much to Oliver's discomfort, so I think it'd be funny if John did reappear and Thea started fliring with him depsite the obvious age difference, but then again hasn't stopped Wild Dog from having a crush on her. Knowing John's character it wouldn't surprise me if he and Thea had a one night stand which could add some tensions between him and Oliver.
More Suicide Squad
Yea this is a no brainer either which needs very little explination. I know they can't use Suicide Squad anymore because of the DC movies but since they you know, kinda suck ass, minus Margot Robbie's Harley Quinn, I say the producers should just say fuck it and do what they want.