"Crisis on Infinite Earths" already boasts an impressive list of confirmed guest stars and cameos. However, according to showrunner Marc Guggenheim, there are few more surprises that have not been announced yet.Responding to a tweet by a fan asking if the crossover event will feature any more cameos, Guggenheim wrote back that several more have yet to be revealed.RELATED: Arrowverse Concept Artist Confirms Kevin Conroy is Kingdom Come’s Batman

The list of special guest stars for the crossover event is massive, and includes Batman: The Animated Series' Kevin Conroy, Black Lightning's Cress Williams, Batman 1966 star Burt Ward, Legends of Tomorrow's Jonah Hex, The Flash's John Wesley Shipp, Birds of Prey alum Ashley Scott, Smallville's Tom Welling and Erica Durance, as well as "Elseworlds" alums Tyler Hoechlin and Elizabeth Tulloch. DC's Legends of Tomorrow star Brandon Routh has been confirmed to appear as Kingdom Come Superman.

"Crisis on Infinite Earths" begins Sunday, Dec. 8 on Supergirl, then continues in Batwoman on Monday, Dec. 9, and then picks up in The Flash on Tuesday, Dec. 10. After a winter hiatus, the crossover concludes on Tuesday, Jan. 14 on both Arrow and DC's Legends of Tomorrow.

KEEP READING: Crisis: One of Kingdom Come's Most Heinous Events Is Part of the Crossover