Crisis on Infinite Earths: Part One

"Things are turning out differently than expected. But one thing is certain. Everything we know... everything there is... and everything there ever was... is doomed."

- Pariah

The episode is the first part of the five-part crossover, ​.

Synopsis
The Monitor sends Harbinger to gather the worlds’ greatest heroes - Supergirl, the Flash, Green Arrow, Batwoman, White Canary, the Atom and Superman - in preparation for the impending Crisis. With their worlds in imminent danger, the superheroes suit up for battle while J'onn and Alex recruit Lena to help them find a way to save the people of Earth-38.

Trivia

 * This episode took place primarily on Earth-1, Earth-38, Earth-16 and Argo City. Plus small appearances from Earth-89, Earth-9, Earth-X, and Earth-66.
 * Lex Luthor, Doomsday, General Zod, Eve Teschmacher, James Olsen, President Plastino, Alana, Malefic J'onzz, Iris West-Allen, Cisco Ramon, Beth Kane, Felicity Smoak and William Clayton were all mentioned, but do not appear.
 * The following episodes were referenced in this episode:
 * The last time Supergirl saved Alana's pet extraterrestrial dragon, Spike from.
 * When Lex Luthor took control of the government in and.
 * Daxamites attacked Earth in and.
 * When James Olsen left the team in.
 * Lena Luthor betrayed Supergirl and Alex, and stole Myriad, only to blame it on Eve Teschmacher from the two episodes prior, and.
 * The Legion returned to the future without their ship in.
 * When Oliver and Sara Lance were presumed dead on the Queen's Gambit from the and Sara returned to Lian Yu in  and later to Star City in.
 * When Ray Palmer interacted with Janis Joplin at Woodstock in.
 * The doomsday protestor is a direct reference to the one in Superman II, holding the exact same sign.
 * This is the first episode of the series to not feature after being promoted to a series regular.
 * This is the first portion of a crossover to not feature  though he was mentioned.
 * This episode featured uncredited cameo appearances from Russell Tovey, Alan Ritchson and Curran Walters.
 * Earth-89, Earth-9, Earth-X, Earth-66 and Earth-38 are wiped out by antimatter, leaving the status of many of their residents unknown.
 * Kara tells Clark, "Krypton isn't just a place, it's a spirit". This is extremely similar to the Marvel movie Thor: Ragnarok, in which Heimdall tells Thor, "Asgard isn't a place, it's a people".
 * Clark lamenting how "i couldn't save her" in regards to his Aunt Alura sounds like the words he spoke over Pa Kent's grave in Superman: The Movie after his foster father died of natural causes.
 * Lois and Kal-El sending Jonathan away from Argo in a pod right before the city was destroyed by antimatter is a reference to Alexander Luthor Jr. being sent from the Crisis DC comic.
 * In addition, it is similar to the way that Kal-El was sent from Krypton, also as an infant, immediately prior to the planet's destruction. Clark and Lois also quote Marlon Brando's Jor-El from Superman: The Movie.
 * Marc Guggenheim states that one of the reasons for Oliver's death was to show that the lives of any of the heroes isn't safe.
 * The Monitor's opening narration is almost exactly the same as the one that explains the DC multiverse on the very first page of Crisis on Infinite Earths by Marv Wolfman and George Perez.
 * The sign that Wil Wheaton held was the exact same sign that a protester wore in Superman III.
 * In Pennsylvania, specifically Pittsburgh, this episode was pushed back to 12:00 am due to the Nightly Sport Call recanting the lastest Steelers Game and then the news.

Goofs

 * Earth-16 Oliver Queen believed Sara died on the Gambit. However, in, Oliver knew Sara survived and referenced a conversation with Ray Palmer in.
 * It's possible Oliver was mind wiped off screen to the timeline intact seeing as this visit happened prior to that episode.
 * Despite The Legion returning to the future with their ship, it makes an appearance in this episode.
 * Joker (Earth-89) was said to be captured by Batman (Earth-89) and is also confirmed to be the same Batman and Joker from the 1989 film, Batman. However, in the film, Batman killed the Joker.

Production
Shooting for began on September 24, 2019.