"Crisis on Infinite Earths: Part Three" is the ninth and midseason finale episode of the sixth season of The Flash, and the one-hundred-twenty-third and most recent episode overall. It aired on December 10, 2019.
During production, the episode was titled "Crisis on Infinite Earths: Hour Three".
This is the second time a character makes a sacrifice to save another character who is destined to die in a possible future. The first was H.R. Wells who sacrificed his life to save Iris by trading his life with her by getting killed by Savitar, and the second is Barry Allen (Earth-90) who trades his life with Barry Allen (Earth-1) to stop the anti-matter from destroying Earth-1.
Cress Williams became immediately starstruck when he stepped onto the set of the Arrowverse's forthcoming "Crisis on Infinite Earths" saga for the first time. "It's like going to a new school", says Williams, who took a break from shooting Black Lightning in Atlanta to spend a week working on the crossover in Vancouver. "I was just really overwhelmed at the pure number of people, and all of these supersuits. I was working with the Flash, two Supermen, most of the cast of The Flash, and some Arrow people. It was just a real hodgepodge, a full room".
For Guggenheim, it was important that Black Lightning appeared in the crossover for more than a glorified cameo, with Williams flying between the two filming locations on the weekends to maximize his availability while Black Lightning's writing staff reduced his role in several episodes to better accommodate his involvement.
Marc Guggenheim noted that the inclusion of Cress Williams' Black Lightning was a particularly challenging one due to the actor having to fly back and forth from Atlanta the primary filming location for Black Lightning to Vancouver, where "Crisis" was filmed. To make things even more difficult, logistically, Williams' costume, specially modified to give off a pulsating electric aura, was expensive to transport between the two filming locations to accommodate Williams' series and the crossover. "His costume is a very involved piece of equipment that has to be traveled (and) has a separate handler that has to travel with it", explained Guggenheim in an interview with Variety. "It was suggested to me at one point, by one of the money people, "Does Black Lightning really have to wear his costume in the crossover?". He has to wear that costume. It just wouldn't be the same if he didn't".
When Barry came back to Iris, he stated that he told her that he'd be running home to her which is a reference to "Runnin' Home to You", the song he used to propose to her.
When absorbing the energy from the Anti-Matter Cannon, Jefferson quotes his school motto.
This is the first time since "Invincible" that a version of Tina McGee has appeared in the Arrowverse.
Frost says about Ralph that it's his first crossover, breaking the fourth wall with the fact that it's actually Hartley Sawyer's first-ever crossover other than a brief appearance in "Elseworlds, Part 1".
Ralph's reaction to seeing the assembly of heroes, "Holy All-Star Squadron", is a reference to the All-Star Squadron, a World War II era offshoot of the Justice Society of America in the comics.
Lucifer mispronounces Constantine's name with what is actually the correct pronunciation of the name in the original comics, a shout-out to fans who were annoyed that it was changed for both the television and film adaptations of the character.
Kara holding Earth-96 Clark as he dies mirrors the iconic Dan Jurgens spread from the Death of Superman story in Superman #75.
Its also a reversal of the cover of the Crisis on Infinite Earths comics. On the cover, Superman is holding a dead Supergirl.
Earth-666 contained a billboard for the DC graphic novel Watchmen that was airing its TV adaption at the time.
Leonard tells the heroes that they have 28 seconds from the destruction of Earth-1 to the destruction of the Waverider, but the gap is actually about 45 seconds. However, it's possible that there was some time overlap during the transportation of the Paragons to the Vanishing Point.
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