A list of crossover episodes which involve characters or plot lines from multiple shows in the shared multiverse. They are arranged chronologically, grouped by season.

2014-2015 Season

Episode from # Episode name Show(s) crossing over
The Flash S1 01. "Pilot" Arrow S3
Barry Allen calls Oliver Queen, saying he needs some advice.
Arrow S3 01. "The Calm" The Flash S1
Oliver Queen takes Barry Allen up on his offer. Barry then visits Starling City to reveal his newfound powers and ask what he should do.
The Flash S1 04. "Going Rogue" Arrow S3
Felicity Smoak visits Barry Allen in Central City to see his superpowers for herself, meets and helps Team Flash, and assists them in defeating Leonard Snart, aka Captain Cold.
07. "Power Outage" Arrow S3
William Tockman, the Clock King, escapes custody in the CCPD and takes several people hostage, including Iris and Joe West.
08. "Flash vs. Arrow" Arrow S3
Oliver Queen, Felicity Smoak and John Diggle head to Central City looking for the boomerang killer, and help Team Flash fight Roy Bivolo, a meta-human who can cause uncontrollable rage in others. Oliver and Barry's differing methods cause tension between the two, and they are forced to fight when Bivolo uses his powers on Barry.
Arrow S3 08. "The Brave and the Bold" The Flash S1
Barry Allen, Cisco Ramon and Caitlin Snow visit Starling City to help Team Arrow defeat assassin Digger Harkness. While there, Cisco meets Detective Quentin Lance, and Barry and Oliver resolve their previous differences.
Vixen S1 01.-06. "Episode 1" • "Episode 3" • "Episode 4" • "Episode 6" Arrow S3 • The Flash S1
Cisco Ramon uses Felicity Smoak's facial recognition software to look for meta-humans outside Central City and finds evidence of Mari McCabe using her animal powers against thugs in Detroit. He nicknames her "Vixen" and gives her whereabouts to Barry Allen, who decides to take backup; he and the Arrow show up at Mari's apartment. When Barry uses her name, she panics and runs away. Flash and the Arrow chase Mari, who uses various animal powers to evade them, including speed, wall-climbing, camouflage, and flight. They eventually talk; Mari explains she was not in Central City for the particle accelerator explosion, a fact confirmed by Felicity Smoak, and refuses their offer of help, threatening them with violence if they return. Flash and the Arrow visit Mari again, offering to help train her if she intends to become a vigilante; she says she is but wants to work things out on her own. She asks about getting a codename and Barry says they call her "Vixen"; he lets slip Cisco's name, giving her a clue as to his identity. (Takes place around the same time as "The Offer".)
The Flash S1 18. "All Star Team Up" Arrow S3
Ray Palmer and Felicity Smoak visit S.T.A.R. Labs to get help perfecting Ray's A.T.O.M. Exosuit, and help Team Flash defeat a swarm of robotic bees.
Arrow S3 19. "Broken Arrow" The Flash S1
Team Arrow and Ray Palmer defeat the meta-human Jake Simmons, aka "Deathbolt", who has come to Starling City thinking no-one can stop him with the Arrow gone. Simmons is imprisoned in the Pipeline, but Cisco and Ray realize he was in Opal City during the dark matter wave, making the source of his abilities a mystery.
The Flash S1 19. "Who is Harrison Wells?" Arrow S3
Cisco Ramon and Joe West head to Starling City to investigate the real identity of Harrison Wells with the help of Quentin Lance. Cisco also meets Laurel Lance and upgrades her sonic device, renaming it the "Canary Cry".
22. "Rogue Air" Arrow S3
Barry Allen decides to move the meta-humans from the Pipeline at S.T.A.R. Labs to the A.R.G.U.S. prison on Lian Yu, to protect them from the plans of the Reverse Flash. He enlists the help of Leonard Snart, but Snart double-crosses the Flash and frees most of the villains. Barry then fights the Reverse Flash, defeating him with the help of Oliver Queen and Firestorm.
Arrow S3 23. "My Name Is Oliver Queen" The Flash S1
Barry Allen briefly visits Nanda Parbat to save the members of Team Arrow, convincing them Oliver still needs their help.

2015-2016 Season

Episode from # Episode name Show(s) crossing over
Arrow S4 01. "Green Arrow" The Flash S2
In a flash-forward to six months in the future, Barry Allen visits Oliver Queen in a graveyard, apologizing for missing a funeral. Oliver vows to kill "him", and asks Barry to leave before weeping over the grave.
05. "Haunted" Constantine (set after its S1)
In a flashback to his time infiltrating Baron Reiter's operation on Lian Yu, Oliver Queen meets John Constantine, saving his life while he is retrieving the Orb of Horus. In the present, Oliver calls in this favour from John to restore the soul of Sara Lance, who has been resurrected from the dead by the Lazarus Pit.
Vixen S2 01.-06. "Episode 1" • "Episode 4" • "Episode 5" • "Episode 6" Arrow S4 • The Flash S2
After Mari confronted Dr. Macalester about his role in Kuasa's plot to steal her totem, Cisco contacts her to assist the Flash and Firestorm to stop Mark Mardon from causing havoc at Monument Point. After being placed in a coma by Mardon, Mari awakens with Chuck at her side. Soon she discovers that another totem from Zambesi Village was stolen. Mari discovers that Benatu Eshu is responsible for the heist and he uses the totem's pyrokinetic abilities against her. Mari seeks out Kuasa and discovers that Eshu was responsible for the massacre of most of the Zambesi in search of the magic totems. With the help of Felicity, the sisters reluctantly work together and they find the Zambesei water totem. After Kuasa's attempt at betrayal is thwarted by Mari, the Atom and Black Canary, they together battle Eshu. Mari defeats (and possibly unintentionally drowns) Eshu, at the cost of Kuasa's life. After the fire totem is destroyed, Vixen meets up with Flash, Green Arrow, Black Canary, and Atom at Coast City, feeling that in Detroit or out, it is her responsibility to protect others.
The Flash S2 08. "Legends of Today" Arrow S4
When Vandal Savage comes to Central City looking for Kendra Saunders, Team Flash ask Team Arrow to help keep her safe, but Carter Hall shows up claiming he and Kendra are reincarnated lovers. Savage follows them, and they learn from Malcolm Merlyn that Savage is an immortal looking for the Staff of Horus, and will stop at nothing until he finds it and kills both Carter and Kendra.
Arrow S4 08. "Legends of Yesterday" The Flash S2
Team Arrow and Team Flash work together to save Kendra Saunders and Carter Hall from Vandal Savage, who is willing to destroy both Central and Star Cities in his quest to kill them. They enlist the help of Malcolm Merlyn, who secretly recovers Savage's remains after he is turned to ash in the final conflict.
DC's Legends of Tomorrow S1 01. "Pilot, Part 1" Arrow S4
Approached by Rip Hunter to be part of his time-travelling team, Ray Palmer seeks Oliver Queen's advice, and decides to join. Sara Lance, given the same offer, spars with her sister Laurel, who encourages her to go and be a hero. She gives Sara a new codename, "White Canary", and a new suit to go with it that doesn't include a mask. Martin Stein, Jefferson Jackson, Kendra Saunders, Carter Hall, Leonard Snart and Mick Rory are also recruited, all in order to stop Vandal Savage from conquering the world in the year 2166. They travel back in time to 1975 to meet Dr. Aldus Boardman, an expert on Savage, whose information would later help Team Arrow and Team Flash defeat Savage in 2015.
02. "Pilot, Part 2" Arrow S4
At their first encounter with Vandal Savage in 1975 Norway, Rip Hunter's team find him selling a nuclear warhead at an illegal arms auction; one of the bidders is Damien Darhk, looking the same as he does in 2015, backed up by H.I.V.E. "ghosts".
Arrow S4 15. "Taken" Vixen (set after its S2)
Mari McCabe visits Star City, using her totem to help Team Arrow find and destroy the source of Damien Darhk's power.
The Flash S2 15. "King Shark" Arrow S4
John and Lyla Diggle visit Star City and help Barry defeat King Shark.
DC's Legends of Tomorrow S1 6. "Star City 2046" Arrow S4
When the team arrives in 2046, they meet Connor Hawke and an old Oliver Queen. And they team up to take down Grant Wilson.
Supergirl S1 18. "Worlds Finest" The Flash S2
While testing the Tachyon prototype to increase his speed, Barry Allen accidentally travels to Earth Thirty-Eight's National City and meets Kara Danvers, helping her to defeat the Silver Banshee and Livewire before she helps him return home split seconds after he left.
Arrow S4 17. "Beacon of Hope" The Flash S2
Brie Larvan escapes from jail and heads to Star City, looking to steal the Palmer Technologies bio-chip embedded in Felicity's spine.
DC's Legends of Tomorrow S1 9. "Left Behind" Arrow S4
When Ray, Kendra and Sara are stuck in 1958, Sara joins the League of Assassins and meets Ra's al Ghul.
Arrow S4 19. "Canary Cry" The Flash S2
Barry visits Oliver at Laurel's grave, apologizing for missing her funeral due to Zoom. Oliver vows to kill Damien Darhk in revenge and asks Barry to leave before weeping over Laurel's grave. (This is the flash forward scene from "Green Arrow".)
DC's Legends of Tomorrow S1 16. "Legendary" Arrow S4 • The Flash S2
Rip brings the team back to Central City in 2016 - but five months after they left. Sara returns to Star City, where her father tells her of Laurel's death. Rip tells Sara they can't go back in time to save her. Sara and Quentin visit Laurel's Grave where Sara reveals it was Laurel that convinced her to join Rip's team, and she will continue for her sister. Meanwhile, Professor Stein reunites briefly with his wife Clarissa.

2016-2017 Season

Episode from # Episode name Show(s) crossing over
The Flash S3 02. "Paradox" Arrow S5
Barry goes to Star City to talk with Felicity about the changes that he has noticed as a result of Flashpoint. Team Arrow are unaffected, except that John Diggle and Lyla Michaels have a son - John Junior - instead of daughter Sara.
DC's Legends of Tomorrow S2 01. "Out of Time" Arrow S5
Nate Heywood notices changes to the timeline, and seeks out Oliver Queen, whom he has worked out is the Green Arrow, to help him find the Legends. They find Mick Rory in stasis on the Waverider under the sea. When they wake him, Mick tells them the Legends were scattered after attempting to stop Damien Darhk from blowing up New York with the Nazis in 1942. Oliver convinces Nate to join Mick in finding the others, while Darhk is revealed to have teamed up with Eobard Thawne.
DC's Legends of Tomorrow S2 03. "Shogun" The Flash S3
Martin Stein and Jefferson Jackson find a secret compartment on board the Waverider and discover a secret message from their old friend Barry Allen that he sent to Rip Hunter from 2056 that Rip was never to tell the team but they listen to it and agree to keep it secret. They listen to the message again in "Abominations", teasing that "A War is Coming".
DC's Legends of Tomorrow S2 05. "Compromised" Arrow S5
Damien Darhk continues his secret partnership with Eobard Thawne though under some hesitation but Damien agrees and becomes a senior adviser to President Ronald Reagan in the 1980s but he meets the younger Martin Stein who tries to confront him but he stabs him altering the timeline but then he faces Sara who threatens him telling him his future, which scares Damien just as Eobard helps him escape and Damien asks Eobard for help to change his destiny, Eobard gives him a Time Sphere and they travel in time to change both their destinies.
Supergirl S2 08. "Medusa" The Flash S3
Barry Allen and Cisco Ramon travel to Earth Thirty-Eight in need of Kara's help. They came to her apartment on her earth, where Barry introduces Kara to Cisco and asks her if she recalls a favor she owes.
The Flash S3 08. "Invasion!" Supergirl S2 • Arrow S5 • DC's Legends of Tomorrow S2
Barry speeds over to Star City to ask for Oliver, Felicity and Diggle's help to go after aliens known as the Dominators according to Lyla Michaels. Thea Queen wants to come out of retirement as Speedy and help too, Barry also decides to call on the Legends for their assistance and he and Cisco travel to Earth 38 for Supergirl's help too seeing as she's a alien which may help, Barry introduces her to the others especially Oliver. Ray shows Cisco his new suit then tells Barry that Snart died a hero. Felicity talks to Cisco over his anger for Barry while Martin and Jax show him the message, along with Oliver, they all discover that it's Barry telling Rip Hunter that he created Flashpoint, Caitlin takes Martin back to his home where he finds that he has a daughter while everyone trains against Supergirl whose too strong for them all, Cisco finds the message and wants Barry to tell everyone about Flashpoint, Barry tells the others especially that Diggle had a daughter, but now has a son. this creates a rift in the team, with Sara reminding Barry that she always wants to save Laurel but she knows she can't due to the implications on her friends. Ray calls Barry's Flashpoint Timeline a Time Aberration. Barry sits out of the mission with Oliver who backs him up while Kara leads the team but the mission becomes a trap and they get brainwashed and Barry and Oliver try to stop them, Wally West helps too before Supergirl hurts him. The Flash and Green Arrow are able to save their friends before some of them get taken away.
Arrow S5 08. "Invasion!" Supergirl S2 • The Flash S3 • DC's Legends of Tomorrow S2
Oliver, Diggle, Thea, Sara and Ray got taken to the Dominators spaceship where they are all put to sleep under a hallucination of what would happen if Oliver, his father and Sara never got on the Queen's Gambit. They eventually discover its a dream world and battle Malcolm Merlyn, Deathstroke and Damien Darhk to escape then they wake up and battle Dominators and try to get away. Meanwhile Felicity brings Cisco to Star City where they try to find them, he meets Curtis Holt, Rory Regan and Rene Ramirez who despises Metahumans and Aliens. she asks for The Flash and Supergirl's help when they discover Dominator technology fell into the wrong hands. They take on a villain whom they nickname Cyberwoman before they find their friends and contact Nate aboard the Waverider to save them as they find out more on the plan.
DC's Legends of Tomorrow S2 07. "Invasion!" Supergirl S2 • The Flash S3 • Arrow S5
Everyone except for Thea regroups in Central City. Nate joins them and reveals that he found footage from the first Dominators Invasion in 1951 and the team suggest they capture one of the Dominators to get information on their plan seeing as they took some of them first. Cisco and Felicity want to time travel in the Waverider, Nate takes Amaya Jiwe and Mick, Oliver tells Kara to sit out of the mission as he feels some normatlity needs restored. Felicity gets sick from the effects of Time Travel but she and Cisco remain on the Waverider where Felicity talks to Cisco again as she can tell that Cisco wanted to get away from Barry. Mick, Amaya and Nate go to find the Dominators. Nate tries out his new Steel Suit that Ray built him. the three Legends get captured while trying to kidnap a Dominator, they get taken by Agent Smith who in the present days tries to go after Barry, Oliver, Ray and Sara, but they overpower his agents and both teams in past and present discover that the Dominators live in fear of Metahumans due to the Justice Society of America in the past but in the present when Barry created Flashpoint as it broke a peace between them and Earth so the Dominators want Barry to surrender himself so they live in peace and they created a Meta Bomb to kill all of the Metahumans. Felicity and Cisco save their friends but when they return to 2016 Central City, Cisco discovers that he changed the timeline, This prompts him to make up and forgive Barry for creating Flashpoint resulting in Dante's death. the team try to persuade Barry not to surrender himself to the Dominators. they battle the Dominators. Sara uses the Waverider's beam to lift the Meta Bomb away so Firestorm can transmutate it. he succeeds and all of the Dominators retreat. The Teams celebrate their victory and Cisco created and interdimensional extrapolator for Kara so she could create breaches to come to their earth if they need her help or they come to her earth if ever she needed her help. Kara, Barry and Oliver have a group hug and Diggle forgives Barry before they all said goodbyes. Caitlin Snow continued to try and help Stein get through to his daughter Lily whom he reveals was the result of a time aberration he caused in 1987. he tells Jax about her after he connects with her but tells him not to tell the rest of their team.
DC's Legends of Tomorrow S2 08. "The Chicago Way" Arrow S5
Eobard and Damien arrive in 1920s Chicago with their new recruit, Malcolm Merlyn to convince Al Capone to let them help him and deal with his nemesis Elliot Ness, Merlyn influences a trap for the Legends for Damien observes them taking the bait, Damien and Eobard capture Sara and Stein, Malcolm reveals to Sara that he's responsible for blowing up the Queen's Gambit and offers her a chance to redo her life but she tells him that no one can change time for their own needs or desires, then Damien takes Stein to talk to Thawne who steals Stein's identity so he can infiltrate the Waverider and steal a piece of an amulet that he collected in 1940s. Merlyn leads some of Capone's men to help expand the search, he battles Sara while Amaya and Mick battle Thawne, who later shows Merlyn and Darhk that the amulet is a compass link to their discovery of the Spear of Destiny.
09. "Raiders of the Lost Art" Arrow S5
Malcolm Merlyn and Damien Darhk travel back to 1967 to find Rip Hunter who has a piece of the Spear of Destiny but when the Legends find them and come into conflict, they cause a Time Abberation where George Lucas quit film school because the Legion scared him off but the Legends manage to convince Lucas to continue directing just in time to battle Merlyn and Darhk but just at that point Eobard Thawne arrives and the Legion kidnap Rip Hunter.
The Flash S3 11. "Dead or Alive" Supergirl S2
While Cicso and Gypsy battled in all of the Multiverse, they end up in Earth-38 and enter CatCo Worldwide Media, where Eve Teschmacher watched and disappeared in to the portal and Eve relips This is why National City got weirder and weirder every day.
DC's Legends of Tomorrow S2 10. The Legion of Doom The Flash, Arrow
The episode was told from the Legion of Doom's point of view, although it references back to both Arrow and The Flash where this story reveals that Eobard and Damien recruited Malcolm straight after the events of Schism. Also as the Legends figure out the speedster, Martin recalls his involvement in events of "Fast Enough" recalling when Eobard was erased. Eobard himself recalls the events of Flashpoint where he was taken out of the timeline by the Flash right after he chose to save his mother and help Eobard captive for months. Hunter Zolomon debuted in the show as Speed Force's enforcer.
Arrow S5 11. "Second Chances" The Flash S3
Oliver calls for some help from Captain David Singh as the Green Arrow, even needing some assistance from The Flash himself when he needed to prove to this to Singh himself.
DC's Legends of Tomorrow S2 12. Camelot/3000 Arrow
Damien Darhk travels back through time with Rip Hunter who was turned evil by the Legion of Doom and leads Darhk to King Arthur's Camelot where Stargirl is protecting her fragment of the Spear of Destiny (Hunter assigned the JSA to each protect a piece of the Spear of Destiny in a different points in Time) while at the same time the Legends follow a lead from Dr Mid-Nite in the future that brings them back to Camelot where they join the Knights of the Round Table, The Legends take Rip as well as Stargirl's piece of the Spear of Destiny, Ray battles Darhk in a sword fight then eventually becomes a knight also Sara kisses Guinevere.
15. Fellowship of the Spear Arrow
17. Aruba Arrow
Supergirl S2 16. "Star-Crossed" The Flash S3
Winn found the interdimensional extrapolator and ran diagnostics on it before giving it back to Kara while claiming he and Cisco could be friends if they lived in the same dimension. Music Meister arrives at the D.E.O. and hypnotizes Supergirl, then snatches her extrapolator and announces his plan to go after the "fastest man alive" before leaving for Earth One. Kara wakes up to find herself in a 1920's nightclub.
The Flash S3 17. "Duet" Supergirl S2
Mon-El and J'onn J'onzz travel to Earth One carrying a comatose Kara to ask Team Flash for help. Music Meister hypnotizes Barry and sends him into the same dream world as Kara, where they are instructed to reach the end of the musical in order to leave. Wally, Cisco and J'onn confront and defeat the Music Meister. Mon-El and Iris later confront him, and he tells them the only way to bring Barry and Kara back lies within themselves. They are later able to awake them via a kiss. Music Meister then reveals his plan all along was to teach them a lesson about love, then fades away to teach his lesson to others. Kara, Mon-El and J'onn then depart for Earth Thirty-Eight.
Arrow S5 22. "Missing" DC's Legends of Tomorrow S1
While flying to Lian Yu, Nyssa mentioned that her father, Ra's al Ghul years ago sent her there where she found Sara, thus Ra's fulfilled the promise he made to future Sara back in 1960.

2017-2018 Season 

Episode from # Episode name Show(s) crossing over
DC's Legends of Tomorrow S3 01. "Aruba-Con" The Flash S4
Nate is seen working alongside Kid Flash in fighting crime in Central City after the Legends are disbanded.
The Flash S4 05. "Girls Night Out" Arrow S6
Felicity Smoak comes to Central City for Iris West's bachelorette party.
DC's Legends of Tomorrow S3 05. "Return of the Mack" Arrow S6
Legends consult with Curtis Holt about a Palmer Technologies watch with Oliver Queen's fingerprints, which turns out to be one belonging to Damien Darhk, whose later resurrected.