- 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.
- 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 and Legends of Tomorrow showrunner Marc Guggenheim being among the criminals in Arkham Asylum nods to his unpopularity among the fans, especially the comicbook community.
- Hide Your Pregnancy: Subverted. 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.
- 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.
- 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.
- 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.
- You Look Familiar: Jeremy Davies who plays Dr. John Deegan previously played Ritchie Simpson on Constantine.
Trivia / Elseworlds (2018)