Marc Guggenheim, the Arrow co-creator who has taken point on running the last two big CW/DC crossover events, told fans during a kind of impromptu Twitter Q&A that they are still doing pickups and weather-related reshoots on "Crisis on Infinite Earths," and that there are still some surprises -- and potentially some cameos -- that fans are not expecting. Between schedules and the extensive needs of the crossover in terms of visual effects and the like, it is not surprising they are still working to finalize the event...but the idea that they are still adding new content has taken some fans by surprise.
One has to assume that any new content they are creating at this stage would either be shot on a green screen and inserted into "Crisis," or something involving one or two actors who could peel away from their main shows to do it...but of course, "Crisis" has gotten so huge, anything feels like it can happen.
You can see Guggenheim's tweet below (and there are a couple more in his timeline for additional context).
"Crisis on Infinite Earths" has loomed over the Arrowverse for years. The series premiere of The Flash featured an allusion to the hero disappearing amid red skies in the year 2024. During the original comics event, red skies were a sign of doom to come to a world during the Crisis. At the end of last season, a couple of things happened: The Monitor (LaMonica Garrett), who had appeared in "Elseworlds," reappeared and revealed that Oliver Queen was destined to die in the Crisis...and the future newspaper at STAR Labs rolled back the expected date of the Crisis from 2024 to 2019.
In the comics, Crisis on Infinite Earths centered on a battle between the combined superheroes (and even some villains) of the DC multiverse and an immortal, cosmic threat known as the Anti-Monitor. Like The Monitor, the Anti-Monitor will be played by LaMonica Garrett in the Arrowverse. As the Anti-Monitor destroys realities, he replaces their positive matter energy with antimatter, growing his own power and sphere of influence. He was eventually stopped by the sacrifices of several heroes, including The Flash and Supergirl, as well as the merging of multiple universes to save reality by becoming a single, unified timeline. Fans have long wondered whether the events of "Crisis on Infinite Earths" might bring Supergirl and even Black Lightning to Earth-1, where the rest of the series take place. The crossover will also feature guest appearances by Tom Welling as Clark Kent, Erica Durance as Lois Lane, John Wesley Shipp as the Flash of Earth-90, Johnathon Schaech as Jonah Hex, Kevin Conroy as Bruce Wayne, and Ashley Scott as The Huntress.
“Crisis on Infinite Earths” kicks off on Sunday, December 8 on Supergirl, runs through a Monday episode of Batwoman and that Tuesday’s episode of The Flash. That will be the midseason cliffhanger, as the shows go on hiatus for the holidays and return on January 14 to finish out the event with the midseason premiere of Arrow and a "special episode" of DC's Legends of Tomorrow, which launches as a midseason series this year and so will not have an episode on the air before the Crisis.