Adapted from one of my blog posts:The actual Crisis storyline started December 8, 2019 (Supergirl), December 9, 2019 (Batwoman), and December 10, 2019 (The Flash); and finishes January 14, 2020 (Arrow, then DC’s Legends of Tomorrow). However, a lot of key parts of the crossover were already in play prior to December 8, 2019. It’s unclear if anything prior to 2018 was originally intended to play into the Crisis. However, anything 2018-2019 definitely is. To avoid minutiae, only the first known use of a particular bit of set-up is noted for the most part. However, given that the Monitor exists solely as part of the crisis event, all appearances of him are noted. I’ve tried to be vague about non-Crisis stuff for people who might want to watch the episodes later, but some spoilers are inevitable. For stuff that’s directly about the Crisis, major spoilers of course.

Additions/corrections welcomed. While I've watched everything to date, I used the Arrowverse Wiki and a few YouTube videos to refresh my memory. Arrow season 1 episode 19 Unfinished Business, April 3, 2013: Lyla Michaels (John Diggle’s ex-wife, now current wife) first appears (Diggle is the main ally of The Hood/Oliver Queen, now Green Arrow). In the comics Lyla Michaels is Harbinger, a pivotal figure in the Crisis on Infinite Earths. Arrow season 1 episode 20 Home Invasion, April 20, 2013: Lyla uses the code name Harbinger. Note: in Arrow’s first seasons the showrunners were largely creating low/non-powered versions of characters who had powers in the comics, and downplaying gadgets for non-powered characters. So it’s likely that at the time that the show’s Lyla was initially intended to be a non-powered version of the comic character. Regardless, this did mean that once the creators decided in fact to do the Crisis, they already had a Harbinger in place. The Flash season 1 episode 1 Pilot, October 7, 2014: We first see a holographic newspaper from the future (2024) with the headline Flash Missing, Vanishes in Crisis. The author and date of the article will fluctuate as the future shifts. This article won’t track all the fluctuations of the newspaper, just the ones that seem the most significant to the Crisis. The Flash season 1 episode 20 The Trap, Apr 28, 2015: Iris West-Allen is now the author of the future newspaper article. Except for the occasional time fluctuation, she will normally be the author of the article. Note: a season 3 storyline dealt the possible death of Iris. I won’t reveal if she survived or if someone took her place, but a version of Iris is currently in play and thus the author of the article. The Flash season 1 episode 23 Fast Enough, May 19, 2015: First hint of a Multiverse (a helmet that appears to belong to Jay Garrick, who in some comic continuities exists on Earth-2). The Flash season 2 episode 2 Flash of Two Worlds, October 13, 2015: First mention of a Multiverse, and first known case of a character arriving from another Earth, who identifies himself as the Flash (Jay Garrick), who is from the Arrowverse version of Earth-2. The Flash season 2 episode 13 Welcome to Earth-2, February 9, 2016: First travel to another Earth in the multiverse (by Flash/Barry Allen and Vibe/Cisco Ramone). First confirmation through visions that other shows exist in the Multiverse: We see still images of Supergirl/Kara Danvers (then on another network, CBS as opposed to CW) and the Flash (also Barry Allen) from the 1990-1991 CBS series (this Flash hereafter called Flash-90 to differentiate him from the main/Earth-1 Flash). Supergirl season 1 episode 18, World’s Finest March 28, 2016: The Flash travels to Earth-38, home of Supergirl, thus establishing that characters can travel to worlds seen on shows from other networks (with season 2 Supergirl moved to CW but her adventures remain on another Earth). Note: it’s beyond the scope of this list to note every instance of inter-Earth/inter-show travel. Only precedents relevant to the Crisis noted. Supergirl season 4 episode 8 Bunker Hill, December 2, 2018: Earth-90, the world of the Flash from the 1990-1991 series is devastated. Flash-90 is on the ground while the Monitor stands over him. The Monitor in the comics is one of the prime movers of the Crisis. Flash-90 gets up and manages to flee (this bit gets repeated a few times; only the first instance noted). The Flash season 5 episode 9 Elseworlds, Part 1, December 9, 2018: Flash and Green Arrow switch bodies (kind of) due to actions from John Deegan, who has been granted abilities by the Monitor. Arrow season 7 episode 9 Elseworlds, Part 2, December 10, 2018: Flash and Green Arrow (still body switched) plus Supergirl travel to Gotham. Working with Batwoman/Kate KIane, one of the villains captured is the Psycho-Pirate (while the comic version was created well before the Crisis, he was a key player in the Crisis).  Flash, Green Arrow, Supergirl, and the now-arrived Flash-90 confront the Monitor, who causes Flash-90 to disappear. The Monitor explains that he’s preparing the heroes for a Crisis. Supergirl season 4 episode 9 Elseworlds, Part 3, December 11, 2018: In another confrontation between Green Arrow, Flash, and Supergirl vs. the Monitor, Green Arrow makes a deal with the Monitor in exchange for keeping Flash and Supergirl safe. In Arkham Asylum, Psycho-Pirate says to Deegan, “Don’t worry, Soctor. Everything is as it should be. The stage is set.” Then, quoting the ad for the comic version of Crisis, “Worlds will live. Worlds will die. And the universe will never be the same.” This is followed by a title screen saying, “Coming Fall 2019” then another saying “Crisis on Infinite Earths”. Arrow season 7 episode 22 You Have Saved This City, May 13, 2019: Green Arrow retires from crime fighting in part to help his wife Felicity raise their daughter. As they are settling in to their new home (so Green Arrow is in his Oliver Queen identity), the Monitor shows up and we learn that Green Arrow’s deal with the Monitor was to act as an agent of the Monitor to protect the mulitiverse when it’s time; that time has now arrived. The Monitor informs him that he has seen the future and watched him die. When Oliver asks for confirmation that he means during this Crisis, the Monitor nods. When Felicity confronts the Monitor he tells her the world needs her daughter. In the future, Felicity tells the Monitor she’s ready. When the Monitor reminds her she can’t return, she tells the Monitor he’s waited a very long time to see him (i.e. Oliver) and the two step through a portal. Flash season 5 episode 22 Legacy, May 14, 2019: After a confrontation between Team Flash and the Reverse-Flash results in another history change, the Reverse-Flash says, “See you next crisis” and runs off. The date on the hologram newspaper turns backward. We don’t see the month or day that it lands on, but the year becomes 2019. Supergirl season 4 episode 22 The Quest for Peace, May 19, 2019: A Martian named Leviathan (later revealed to be the brother of J'Onn J'Onzz, the Martian Manhunter) arrives on Earth, where he’s greeted by the Monitor, who tells him he brought him here. The Monitor then visits Lex Luthor for as yet unrevealed reasons. DC’s Legends of Tomorrow season 4 episode 16, Hey, World! May 20, 2019: The Legends perform a stage play as part of their latest mission. The Monitor is in the audience eating popcorn but does not intervene. The Flash Season 6 episode 1 Into the Void, October 8, 2019: The Monitor visits Barry and Iris and claims to have needed to destroy a video important to them to discourage a particular course of action. He tells Barry that he’s destined to die in the Crisis on December 10, 2019. The Flash Season 6 episode 2 A Flash of the Lightning, October 15, 2019: To get a second opinion, Flash tries running to the future to the day after his death but hits an anti-matter field and is injured. Making it to Earth-3, he consults with Jay Garrick, who says he’s also noticed a danger to the multiverse. He provides a means for Barry to project his mind to the future, where he sees his friends killed by a wave of anti-matter and his own subsequent death. While he’s recovering, Jay’s wife Joan reads to him the poem A Flash of the Lightning, which was also quoted in Crisis on Infinite Earths #8, the issue that focussed on the Flash’s fate. Barry and iris argue over Barry’s apparent willingness to die, but he later convinces her that he doesn’t want to die. He’s just prepared in the same way a cop is. Arrow season 8 episode 1 Starling City, October 15, 2019: Oliver travels to Earth-2 on a mission to recover dwarf star matter. With that world’s Oliver deceased, he starts to get involved with counterparts of his family, including Earth-2’s version of his mother Moira. This and other actions causes the Monitor to warn him not to interfere with the lives of Earth-2 residents beyond what is needed to complete his mission. He enlists the aid of Earth-2’s versions of the Hood and Black Canary (Laurel Lance, a former enemy of Oliver’s as the Black Siren until she reformed and returned home) as well the Earth-1 John, who had learned of the Crisis from Felicity and had travelled to Earth-2 using a device given to him by Cisco.  They defeat the Dark Archer, who has the dwarf star matter. Hours later, just after Oliver finishes visiting the Dark Archer at a holding cell, the Crisis arrives on Earth-2, and the police station is surrounded on all sides by anti-matter. The anti-matter kills The Earth-2 Dinah Drake, Rene Ramirez, Moira Queen, and Dark Archer, as well as probably most of the other residents of Earth-2 off screen, but John triggers the portal home and he, Oliver, and Laurel escape through it. Thus far Laurel is the only confirmed native survivor of the destruction of Earth-2, though it’s possible that other metahumans escaped on their own devices and took others with them.

The Flash Season 6 episode 3 Dead Man Running, October 22, 2019: Barry tells Team Flash about the Crisis but at first leaves out the part about his dying. Things happen to get him to reconsider (and Killer Frost figures it out anyway) so he later tells them the rest. Cisco gains a reluctant ally in Nash Wells, the newest Harrison Wells counterpart.

Arrow season 8 episode 2 Welcome to Hong Kong[b], October 22, 2019: [/b]Oliver, John, and Laurel arrive on Earth-1 in Hong Kong, initially separated from each other. The Monitor lectures Oliver about disobeying him by interfering with things on Earth-2, including saving Laurel. He tells Oliver to Bring Dr. Robert Wong to him but refuses to say why. Reconnecting with John and Laurel, Laurel is in denial about the fate of Earth-2 and heads off in search of a contact to send her back to fix the now-damaged portal device and send her back to Earth-2.  Oliver and John team with Katana, who has heard of the Monitor and warns him not to follow the Monitor, which Oliver is more inclined to do since he thinks that staying too long might have somehow brought the Crisis to Earth-2. Lyla showing up to help Laurel, claiming that John sent her, though Laurel is surprised she got to Hong Kong so fast. Laurel's contact fixes the device but is able to return her to Earth-2 because it's no longer there. Lyla has a heard to heart with her about survivor's guilt. After Katana is nearly killed, Green Arrow decides not to hang over Wong to the Monitor right away. However, Lyla meets with the Monitor and hands Wong over; it's clear they've known each other for a while. They argue about Monitor about withholding information about Earth-2, which could have gotten her husband killed.

The Flash Season 6 episode 4 There Will be Blood, October 29, 2019: Members of Team Flash deal with Barry's impending death. Cisco, teaming with Barry and Nash, to obtain a cure for a dying Dr. Ramsey, initially hides the cure because it could also protect barry from anti-matter, but later relents and gives it to Barry. The Elongated Man/Ralph Dibney is initally too depressed to take on a case but eventually embarks on it. Barry's adoptive father joe West braks down over his son's impending death. Barry despite reservations from his hiding the cure, goes with his original choice of Cisco to lead the team after his death. Nash is able to use holographic technology to trace a path to a storage area. Note: It's likely but not confirmed that Nash will become the Pariah (played by the same actor). As the Pariah is a key Crisis figure, should this prove to be the case, his coverage on this page will be expanded.

Arrow season 8 episode 3[b] Leap of Faith, October 29, 2019: [/b]Green Arrow, arriving in Nanda Parbat to consult Nyssa about the Monitor instead encounters his sister Thea (Speedy) and tells her about the Crisis. The two of them meet up with Talia, who initially seems interested in helping Green Arrow learn more about the Monitor but ultimately doublecrosses him. John confides to Lyla that he's still shaken from witnessing a universe being destroyed. Oliver suspects that the Monitor may be an enemy. Possibly brought to the present by the Monitor. Oliver's children Mia Smoak and William Clayton, and John Diggle's adoptive son Connor Hawke, all from 2040 appear.

The Flash Season 6 episode 5 Kiss Kiss Breach Breach, November 5, 2019: Trapped in a cave-in with Joe West (Barry Allen's adoptive father), Nash is surprised to learn Joe has heard of the Monitor. After they're freed by the elongated Man (Ralph Dibny), Nash claims to have a way to save Barry.


Arrow season 8 episode 4 Present Tense[b], November 5, 2019:[/b] Oliver tries to gain info about the Crisis from the future youth, but they can't provide much help. he also enlists Curtis Holt's aid in building a weapon against the Monitor. The Monitor tells Sarah he can bring back Earth-2 if she betrays Oliver. 
The Flash Season 6 episode 6 License to Elongate, November 19, 2019: Nash teams with reformed criminal turned reporter Allegra Garcia. She helps him break the Monitor's wall, a bit reluctantly after she learns he plans to kill the Monitor.

Arrow season 8 episode 5 Prognost, November 19, 2019: Laurel learns that Lyla is a Monitor agents. Oliver, John, Laurel, and the youth head to Russia to obtain necessary material to stop the Monitor. Returning to Star City, Laurel tells Lula she won't take a deal that requires backsliding into her criminal ways and reveals she's told Oliver and John about Lyla. Oliver, John, and Luarel are shot with tranq darts.

The Flash Season 6 episode 7 The Last Temptation of Barry Allen, Pt. 1, November 26, 2019: having learned that Barry is the Flash, Allegra encourages Iris to start on the newspaper story about Barry's disappearance that she's destined to write. Barry, infected by cells by Ramsey Ronno, finds himself being corrupted in a dream state, with Ramsey, having learned both the Flash's identity and about the Crisis, tempts Barry with the power to survive the Crisis, albeit under Ramsey's control.

Arrow season 8 episode 6 Reset, November 26, 2019: Oliver and Laurel find themselves in a pocket reality where Quentin Lance is still alive, but which resets after Quentin dies. Laurel is able to leave when she says a proper good-bye to Quentin, but Oliver is only able to leave when he fully accepts Quentin's passing and my extension his own impending death. this is confirmed in an encounter with Lyla, who admits to have been working for the Monitor for a while. She insists that the Monitor is not his enemy. The two of them and other allies wind up on Lian Yu, the island where Oliver began his path to becoming Green Arrow,

Batwoman season 1 episode 8 A Mad Tea-Party, December 1, 2019: On December 9, 2019, 11:58 pm, Nash, at the Monitor's wall, makes a deal with a voice behind the wall and is transformed.

Supergirl season 5 episode 8 The Wrath of Rama Khan, December 1, 2019: The Monitor appears before J'Onn J'Onzz, who has managed to get his brother to reform, and tells him that bringing Leviathan to Earth was a test that J'Onn has passed, and he is now ready for the Crisis. The Monitor goes to Lex Luthor, who he has apparently brought back from the dead in readiness for the Crisis. With a minor captioning difference, the Batwoman sequence above is repeated.

The Flash Season 6 episode 8 The Last Temptation of Barry Allen, Pt. 2, December 3, 2019: Shortly before midnight on December 9, Barry gathers his friends and family together; Killer Frost reverts to her Caitlin Snow persona, feeling that she should be the one to spend the last few hours with Barry. The people present say their good-byes and then at midnight the skies turn red, signalling the Crisis has arrived. The sequence from Batwoman then repeats again, minus the "Central City" caption as the entire episode takes place there. Since that sequence happens two minutes earlier, it's likely what brings the Crisis to Earth-1.


Arrow season 8 episode7 Purgatory, December 3, 2019: Team Arrow learns they need to retrieve a device on the island. John and Lyla argue about the Monitor.  Additional allies arrive by plane carrying plutonium, which is needed for the device but which may be what temporarily brings foes and an ally back from the dead; they apparently return to the grave when the device is retrieved and activated by Lyla, who disappears. Oliver says his good-byes and Lyla, now the Harbinger returns, the Crisis having arrived. The sequence from Batwoman repeats once more..

Beyond possible tweaking/editing, this concludes this blog post. Episodes of Legends of Tomorrow taking place before Crisis but airing after will not be covered as they will be viewed with the hindsight of the Crisis from the audience's perspective.