The CW will re-air the entire "Elseworlds" crossover event on January 7 and 8, according to their latest primetime listings.
The story, which played out over three nights on The Flash, Arrow, and Supergirl earlier this month, centered on a villain who obtained the Book of Destiny, allowing him to rewrite reality. His first order of business? Pulling a Freaky Friday on Green Arrow and The Flash, so that the whole world thought they were one another, and they had swapped powers and appearances.
The only way to convince people they were telling the truth was to retreat to Earth-38 and get some help from Supergirl and Superman, which ultimately pitted the group of them (and their supporting casts) against The Monitor (LaMonica Garrett) while introducing the city of Gotham and the character of Batwoman (Ruby Rose).
The crossover brought season-high ratings to The CW's DC shows, as it tends to do every year. This season it also aired after the nominal season finales for the shows, so that "Elseworlds" served as the final episodes of 2018 for all three series.
DC's Legends of Tomorrow did not participate in the crossover, and it was explained in-story that their own reality had been warped by unrelated events, and that a more violent and self-absorbed version of the Legends simply ignored messages from the other heroes calling for help. By the time the Legends were restored, those messages had apparently either been lost, or the "Elseworlds" story had resolved itself.
The tale set the stage for -- and included a teaser for -- next year's crossover, "Crisis on Infinite Earths," an adaptation of DC's biggest and most ambitious crossover story of all time in the comics. Given the scope of "Crisis" and its impact on characters like Supergirl and The Flash in the comics, it is likely that the Legends (and anybody else they can recruit) will take part in the crossover next year.
"Crisis on Infinite Earths" dealt with the arrival of the Anti-Monitor, essentially the Monitor's doppelganger from the anti-matter universe. Since the antimatter universe is void, controlled entirely by the Anti-Monitor, and not split into fragments, the Anti-Monitor was easily able to swallow up individual universes within the matter universe to weaken the Monitor and expand his cosmic empire. In the comics, the Crisis brought the end of the DC mutiverse, merging all of the various worlds of DC Comics into a single universe with a shared history.
The first two parts of "Elseworlds" will air on Monday, January 7, at 8 p.m. ET/PT and 9 p.m. The following day, the Supergirl finale will air at 8 p.m. ET/PT, followed by a one-hour special, EA Sports Madden NFL 19 Classic.