Crisis on Infinite Earths: Part Four

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

Synopsis
Stuck in the Vanishing Point, the Paragons search for a way to escape. The futility of the situation is compounded by The Flash's disappearance. However, hope appears in the form of Oliver, who reveals that he has become something else. Meanwhile, the origin stories for The Monitor and Anti-Monitor are revealed.

Main cast

 * Stephen Amell as Oliver Queen/The Spectre
 * David Ramsey as John Diggle
 * Rick Gonzalez (credit only)
 * Juliana Harkavy (credit only)
 * Katherine McNamara (credit only)
 * Ben Lewis (credit only)
 * Joseph David-Jones (credit only)
 * LaMonica Garrett as Mar Novu/The Monitor and Mobius/Anti-Monitor

Special appearance by

 * Katie Cassidy as Laurel Lance
 * Jon Cryer as Lex Luthor
 * Ezra Miller as Barry Allen/The Flash

Special guest star

 * Grant Gustin as Barry Allen/The Flash
 * Caity Lotz as Sara Lance/The Canary/White Canary
 * Brandon Routh as Ray Palmer
 * Tyler Hoechlin as Clark Kent/Superman and John Deegan/Superman
 * David Harewood as J'onn J'onzz/Martian Manhunter
 * Elizabeth Tulloch as Lois Lane
 * Ruby Rose as Kate Kane/Batwoman
 * Melissa Benoist as Kara Danvers/Supergirl

Guest starring

 * Osric Chau as Ryan Choi
 * Stephen Lobo as Jim Corrigan
 * Melanie Merkosky as Xeena

Uncredited

 * Katrina Law as

Production

 * Production for began on September 24, 2019.
 * Filming for the crossover had completed by November 8, 2019, with some reshoots and minor filming still needing to be completed.

Trivia

 * The part of the Crisis on Infinite Earths crossover was co-written by Marv Wolfman, who co-wrote the original Crisis on Infinite Earths comic in addition to co-creating the characters who made their debut in the novel including Harbinger, The Monitor, Pariah and the Anti-Monitor.
 * This part along with 's part in the Crisis on Infinite Earths crossover will both air on Grant Gustin's 30th birthday.
 * Oliver Queen died in this episode and sacrificed himself to rebuild the multiverse.
 * Ezra Miller's version of Barry Allen/The Flash is from the DC Extended Universe films seen in Batman v Superman: Dawn of Justice, Justice League, and the upcoming Flash movie. This marks the first time that the DCEU Films and Arrowverse have crossed over.