The Arrowverse season finales all set up the impending "Crisis on Infinite Earths." Inspired by Marv Wolfman and George Pérez's classic comic book miniseries, this promises to be the biggest event in the history of the Arrowverse. It will air as a five-hour event spread over two quarters, and promises to transform the lives of DCTV's greatest heroes.
The Arrowverse has been setting up "Crisis on Infinite Earths" for five years, ever since the pilot episode of The Flash. That featured a scene in which Harrison Wells, in reality Eobard Thawne or the Reverse-Flash, entered his Time Vault and contemplated a newspaper article from the future. The main headline read "Flash Missing, Vanishes in Crisis." Beneath was a second, "Red Skies Vanish." Both of these were allusions to Crisis on Infinite Earths, where the red skies were a sign of a reality's imminent destruction, and Barry Allen sacrificed himself to prevent his world being consumed by antimatter. Over the years, The Flash has gradually revealed details of that ominous future, hinting at a cosmic event in which Barry was assisted by the likes of Green Arrow, the Atom, Hawkgirl, Supergirl, and Batwoman.
Last year's "Elseworlds" event was essentially pure setup for "Crisis on Infinite Earths," with the Monitor testing all of reality in order to decide if the Arrowverse's heroes were up to the challenge of saving the entire Multiverse. It also introduced the Arrowverse version of Psycho-Pirate, a character who worked for the Anti-Monitor in the comics and was one of the secondary villains. An inmate at Arkhum Asylum, Psycho-Pirate clearly already knew what was coming. "Don't worry, Doctor," he assured another inmate at the end of the event. "Everything is as it should be. The stage is set. Worlds will live. Worlds will die. And the universe will never be the same."
The season finales of all four Arrowverse shows continued the buildup to "Crisis on Infinite Earths," featuring sometimes subtle and sometimes overt cameos from the Monitor. Let's take a look at all this latest setup.
The Flash Season 5
The Flash season finale, "Legacy," was an absolutely essential step along the road to "Crisis on Infinite Earths." This season was all about Eobard Thawne carefully orchestrating a change to the timeline, and it had dramatic repercussions; in one chilling scene, the AI Gideon summoned that infamous newspaper article discussing the Flash's disappearance during the Crisis. The dates began to change, with "Crisis on Infinite Earths" moving back from 2024 to 2019.
We currently don't have enough information to work out quite why Thawne's plan had this effect. Thawne's goal was to destroy the dagger of a villain named Cicada, which contained power-dampening properties, and in the future had been used to restrain him while he awaited his execution. Presumably in the original timeline, Cicada's dagger was originally used to restrain someone else, someone tied to the Crisis, and the most logical candidate is Psycho-Pirate. At the same time, though, this is just guesswork; the reality is that Thawne's Arrowverse timeline doesn't quite make sense. Thawne only escaped the Death Penalty because of the change to the timeline, and yet this all appeared to happen to a version of Reverse-Flash who had not experienced the Crisis yet. It's possible this is just a logical mistake - The Flash's time travel adventures haven't always been thought through to the nth degree - but it may suggest there are other variables that have yet to be even hinted at.
Tragically, the change to the timeline also led to the Flash's daughter, Nora, being erased from history. This is presumably because, in the new timeline, the Flash is destined to disappear before Nora has been conceived. Hopefully the timeline can be adjusted once again, bringing another version of Nora back.
Arrow Season 7
The Arrow season 7 finale, "You Have Saved This City," also prepared the Arrowverse for the Crisis. This season has been split between two times, the present and a future timeline in which Oliver Queen had passed away years ago. In the present, the season ended with Oliver Queen and his team emerging triumphant, and the Green Arrow retiring with his beloved Felicity. Several months later, after the birth of their daughter Mia, they were unexpectedly contacted by the Monitor. The cosmic being materialized in the Queens' living room in order to cash in on the favor Oliver owed him after "Elseworlds," and cautioned that this would lead to Green Arrow's death. "I cannot prevent his passing," the Monitor told a heartbroken Felicity. "But he can prevent the deaths of countless more, including you and your daughter."
The flashforward section revealed that it was set in a post-Crisis universe, one in which Green Arrow sacrificed himself to save the Multiverse. This was done in artistic style, with a shot of Oliver's gravestone, which confirmed he is destined to die in 2019. At the end, the Monitor appeared to the future version of Felicity, offering to take her to her husband's side. Ominously, Felicity did not expect to return from this experience, but was willing to embrace it because she longed to see her husband one last time, and believed her daughter was now safe.
Supergirl Season 4
Supergirl season 4 finally introduced the Arrowverse's version of Lex Luthor, played by the excellent Jon Cryer, and the season finale was the story of Lex Luthor's downfall. Luthor's plans fell apart because of Supergirl and her friends, and he appeared to choose suicide over surrender; in reality, the madman teleported away to a safehouse, a secret base underneath his childhood tree-house. Unfortunately for Lex, his sister Lena figured out where he was going to go, and greeted him there - with a gun. She shot him twice in the chest, killing him.
The final scenes saw the Monitor intervene in the events of Supergirl, just as in all the other shows. He appeared in National City accompanied by a hooded figure dressed in black, and told the stranger he had brought him to Earth so he could avenge himself upon the brother who had wronged him. Although the episode itself didn't name him, this figure was credited as Malefic J'onzz, brother and arch-nemesis of J'onn J'onzz. Then, the Monitor teleported into Luthor's secret base and stood in front of his body, summoning temporal energy. The clear implication is that he was resurrecting Lex Luthor, who presumably plays a role in the Monitor's plans.
Legends of Tomorrow Season Season 4
Finally, Legends of Tomorrow has always been the most loosely-connected of the Arrowverse shows, happily embracing a style and tone all of its own. That was neatly signified in the season 4 finale, "Hey, World!," which featured a hilarious scene in which members of the Legends dressed up as Supergirl, Flash, and Green Arrow in order to do a TV spot promoting a monster amusement park, and complained that the other heroes had refused to help out. The Monitor made a very brief appearance in Legends of Tomorrow, standing in the crowd at the "Superheroes Vs. Monsters" show. He didn't look best pleased by it, for his own inscrutable reasons. Of all the tie-ins, this was the most subtle, and is likely to be the least significant.
In the comics, "Crisis on Infinite Earths" saw the Monitor assemble a team of heroes and villains from across time and space. The Monitor was morally ambiguous, working to save the entire Multiverse and so not caring whether or not his chosen agents were good guys or bad guys. It seems the same is true in the Arrowverse as well, given the Monitor appears to have chosen a handful of key operatives with wildly different moralities; Green Arrow, future Felicity, Lex Luthor, and even Malefic J'onzz. It seems safe to assume the Flash, too, will be numbered among the Monitor's warriors, given he's the hero who - right now - still appears destined to disappear.