Maybe Flashpoint will be the crossover. Flashpoint won't be until later in the season. Throughout the 4 shows we see the ripple effects of Flashpoint and characters hinting at it but not revealing what actually happens. Then when the crossover happens we see the events of Flashpoint and what caused those changes. Arrow Of course Arrow gets better writers. Season 5's flashbacks will even be centered on Robert Queen as the Arrow instead of island flashbacks to switch it up a little. Robert Arrow ends up on Earth-1 somehow. He sees that Oliver has grown soft and ignored his mission. He decides to kill who he sees as the biggest issue: Felicity. But after a few episodes of conflict Oliver and Robert team up to take on a villain but Robert is injured fatally. He then gives Oliver The List which contains the pages that Oliver burnt on the island. He says he's proud of what Oliver has become but also that Oliver needs to focus. Oliver is then faced with a conflict: become more like Robert or stay the more happy GA. He is pushed towards the more Arrow-y side due to losing Felicity but due to some comforting from Black Siren (who is now good) he becomes the full-fledged Green Arrow. On Legends we see Snart back. But not as Captain Cold. No, this version is Citizen Cold. It's not explained until a later that due to an event dubbed the Flashpoint Paradox the Legends now have Citizen while Captain Cold is running around central robbing shit. The Legends also have to go around fixing anomalies while also dealing with the JSA thing. Also, Jay Garrick is now on the team because his Earth was merged with Earth-1 after Flashpoint and he helps to found the JSA. On Supergirl, Kara, MM, Maxwell Lord, and maybe someone else (Cat maybe?) are the only ones to remember not being on the same Earth as the Flash.