- Acting for Two: Tyler Hoechlin plays Superman and Deegan in Superman's form.
- Actor-Inspired Element:
- Darkhorse Casting: Ruby Rose's casting as Batwoman came out of left field for many, particular because some see her as being above a show on The CW.
- Deleted Scenes: Many, but the most notable is the attempt to put Stephen Amell in the Flash intro.
- Doing It for the Art: The real tattoos on Ruby Rose's right forearm and hand were covered in makeup and a new tattoo (a tree) was created in their place. This was not strictly necessary, since the new tattoo is never brought up specifically or shown in great detail.
- Fake American: Australian Ruby Rose plays the American Kate Kane.
- Fandom Nod:
- Earth-90 Flash greeting Diggle as an old friend but noting that he's 'not wearing [his] ring' nods towards a long-held fan theory that Diggle will become a Green Lantern.
- When Oliver wakes up in Barry's life, he immediately assumes it's Barry's fault somehow for messing with the timeline so much.
- A character named after former Arrow showrunner Marc Guggenheim being among the criminals in Arkham Asylum nods to his status as a Scapegoat Creator among the fanbase and the public in general.
- Milestone Celebration: With the DC Extended Universe mired in problems, it falls to this special to provide a proper celebration of the 80th anniversary of Superman's creation, plus the 40th of the 1978 film.
- Name's the Same: There's an inmate at Arkham Asylum who's named after one of the main creators of the Arrowverse, Marc Guggenheim.
- Promoted Fanboy: LaMonica Garrett has been a lifelong fan of comics, and was very familiar with the character of The Monitor (primarily through Crisis on Infinite Earths) even prior to getting the role.
- Real-Life Relative:
- Recycled Set: The Kent farm on Earth-38 is the same one used in Smallville.
- Trolling Creator: Stephen Amell released a picture of him hanging out with Tom Welling and Michael Rosenbaum, ie Clark and Lex from Smallville, and saying he was very excited about whatever they were doing together, raising hopes that the special would do Arc Welding with the series as another Earth. It actually just uses the same farm set. Then the fans got trolled again as because the next year, Smallville ultimately participated in an Arrowverse crossover, after all.
- Troubled Production: Averted by design; filming Crisis on Earth-X was by all accounts very grueling as they had to coordinate and juggle around the four show's different schedules. For this year they decided to make things easier by leaving the Legends out of the story (the decision was later poked at during a Legends of Tomorrow episode)
- What Could Have Been: Guggenheim thought about using the crossover to revive Sara Diggle, but couldn't make it fit here.
- Why Fandom Can't Have Nice Things: Ruby Rose had to close her Twitter account and the public comment section for her Instagram, thanks to the cyber-bullying she suffered from some rabid fans who thought she wasn't fit to be Batwoman (the reasons cited, apparently, were because Rose is non-binary and not Jewish). The fallout spilled over to her series as well, which has been consistently derided by those same people, even though professional critics say it is not as bad as the fandom make it out to be.
- Written-In Infirmity: Elizabeth Tulloch was five to six months pregnant when she was shooting her scenes as Lois Lane. Lois announces her pregnancy to Kara in the episodes denouement.
- You Look Familiar: Jeremy Davies, who plays Dr. John Deegan, previously played Ritchie Simpson on Constantine.
Trivia / Elseworlds (2018)