Crisis on Infinite Earths is the name of the sixth annual Arrowverse crossover event between , , , , and . Additionally, events in the episode "" and a two-issue comic, , tie into the crossover. It began over three nights in December 2019 from December 8 to December 10 and concluded on January 14, 2020.
- Tiahra Allen as Sara Diggle
- Stephen Amell as Oliver Queen/Green Arrow/Spectre and Oliver Queen/Green Arrow
- Audrey Marie Anderson as Lyla Michaels/Harbinger
- Brec Bassinger as Stargirl
- Manu Bennett as Slade Wilson (archive footage)
- Melissa Benoist as Kara Danvers/Supergirl
- April Bowlby as Rita Farr
- Katie Cassidy as Laurel Lance
- Tom Cavanagh as Dr. Harrison Nash Wells/Pariah
- Osric Chau as Dr. Ryan Choi
- Kevin Conroy as Bruce Wayne
- Jon Cryer as Lex Luthor
- Erica Durance as Alura Zor-El and Lois Lane
- Tom Ellis as Lucifer Morningstar
- LaMonica Garrett as Mar Novu/The Monitor and Mobius/Anti-Monitor
- Rick Gonzalez as Rene Ramirez/Wild Dog
- Marcello Guedes as John Diggle, Jr.
- Diane Guerrero as Crazy Jane
- Grant Gustin as Barry Allen/The Flash
- Reina Hardesty as Joslyn Jackam/Weather Witch
- David Harewood as J'onn J'onzz/Martian Manhunter
- Juliana Harkavy as Dinah Drake/Black Canary
- Raul Herrera as Sargon the Sorcerer
- Tyler Hoechlin as Clark Kent/Superman and Superman (John Deegan)
- Benjamin and Elias Hogewoning as Jonathan Kent
- Camrus Johnson as Luke
- Pam Kearns as Doris
- Katrina Law as Nyssa al Ghul (vision)
- Chyler Leigh as Dr. Alex Danvers
- Stephen Lobo as Jim Corrigan
- Caity Lotz as Captain Sara Lance/White Canary
- Jes Macallan as Ava Sharpe
- Nicole Maines as Nia Nal/Dreamer
- Neal McDonough as Damien Darhk (archive footage)
- Katie McGrath as Lena Luthor
- Katherine McNamara as Mia Smoak/Blackstar
- Derek Mears as Earth-19 entity
- Melanie Merkosky as Xneen
- Dina Meyer as Oracle (voice)
- Ezra Miller as Barry Allen
- Wentworth Miller as Leonard (voice)
- Matt Nable as Ra's al Ghul (archive footage)
- Griffin Newman as Trivia host
- Danielle Panabaker as Dr. Caitlin Snow/Frost
- Candice Patton as Iris West-Allen
- Amanda Pays as Dr. Tina McGee (archive footage)
- Eileen Pedde as President of the United States
- Dominic Purcell as Mick Rory and Mick Rory/Heat Wave
- David Ramsey as John Diggle/Spartan
- Jesse Rath as Querl Dox/Brainiac 5
- Alan Ritchson as Hawk
- Ruby Rose as Kate Kane/Batwoman and Kate Kane
- Brandon Routh as Dr. Ray Palmer/The Atom and Clark Kent/Superman
- Matt Ryan as John Constantine
- Hartley Sawyer as Ralph Dibny/Elongated Man
- Johnathon Schaech as Hex
- Ashley Scott as Huntress
- John Wesley Shipp as Barry Allen/The Flash
- Azie Tesfai as Kelly Olsen
- Russell Tovey as The Ray
- Elizabeth Tulloch as Lois Lane and Lois Lane's Earth-75 doppelgänger
- Carlos Valdes as Cisco Ramon/Vibe
- Joivan Wade as Victor Stone
- Curran Walters as Jason Todd/Robin
- Burt Ward as Dick Grayson
- Tom Welling as Clark Kent
- Wil Wheaton as Earth-38 doomsday protestor
- Cress Williams as Black Lightning
- Marv Wolfman as Marv
- Robert Wuhl as Alexander Knox
- Nick Zano as Dr. Nate Heywood
- The title of this crossover, Crisis on Infinite Earths, is also the title of a limited series published by DC Comics from 1985 to 1986.
- Following "" and "", The CW aired a set of TV specials to promote the crossover and reveal behind the scenes details titled .
- This was the first crossover:
- Where the title of the crossover was revealed at the end of the previous crossover ().
- To consist of five episodes.
- To have a one-month break between some of the episodes.
- The break was accounted for within the crossover.
- To have major tie-ins with episodes of and that aired before the crossover.
- To have a tie-in comic book series. The series is titled . It was two issues long and both issues contained "an in-canon story that ties directly into the crossover narrative" and "characters and concepts that couldn’t be included in the crossover."
- To have an aftershow. The aftershow was titled .
- Brandon Routh reprised his role as Superman, having previously portrayed the character in the 2006 film Superman Returns. The iteration of Superman that Routh portrayed is the same character but is now based on the Kingdom Come storyline.
- All currently airing Arrowverse television series will deal with the fallout from this crossover in the remainder of their current seasons.
- Both Michael Rosenbaum and Alan Ritchson were offered the chance to reprise their roles as Lex Luthor and Aquaman respectively from the television series Smallville in this crossover. However, Rosenbaum declined and Ritchson had to decline due to scheduling issues.
- Similarly, Cameron Cuffe was offered the chance to reprise his role as Seg-El from the television series Krypton. However, like Ritchson, he had to decline due to scheduling issues.
- Nicolas Cage was also reached out to, presumably to portray a version of Superman, a role he was set to portray in the canceled film Superman Lives.
- Ritchson did ultimately appear in the crossover, albeit in an uncredited cameo as Hank Hall from the television series Titans.
- Despite Eobard Thawne playing a huge role in Crisis in the original timeline, he did not appear in this crossover. Regarding his absence, Marc Guggenheim said: "I guess what it really comes down to is not being beholden to a headline from six years ago that was not written by any of the showrunners involved in the crossover. A lot of things drive our stories, and a lot of things determine what choices we make. To me, tracking toward a headline written six years ago is literally the definition of ‘the cart driving the horse.’ We’ve had Reverse-Flash so prominent in the Arrowverse over the years, including in last year's crossover and the crossover before that. I love the character and I love Tom [Cavanagh] as a person, and I certainly love Matt Letscher's version, but you have to make choices." 
- So far, this crossover had the most series regulars absent as there were 16 series regulars who were absent. The series regulars who didn't appear in the crossover were:
- - Andrea Brooks (Eve Teschmacher and Hope), Julie Gonzalo (Andrea Rojas/Acrata), and Staz Nair (William Dey).
- - Meagan Tandy (Sophie Moore), Nicole Kang (Mary Hamilton), Elizabeth Anweis (Catherine Hamilton-Kane), and Dougray Scott (Jacob Kane)
- The Flash - Danielle Nicolet (Cecile Horton) and Jesse L. Martin (Joe West)
- Arrow - Ben Lewis (William Clayton) and Joseph David-Jones (Connor Hawke)
- - Maisie Richardson-Sellers (Charlie), Tala Ashe (Zari Tarazi), Courtney Ford (Nora Darhk), Olivia Swann (Astra Logue), and Amy Pemberton (Gideon).
- It's mentioned that "nothing will be the same". Out-universe this also applies to the title cards. There is no longer narration prior to the "previously on" segments. Instead, the time now goes into 12-second title sequences.
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