That's because actress and dancer Cassidy Alexa's character seemed, from the clues around her, to be the fan-favorite Batman villain Harley Quinn, who last appeared in live-action form in the short-lived CW series Birds of Prey (in which she was played by Ferris Bueller's Day Off star Mia Sara, and by Twin Peaks star Sherilynn Fenn in an unaired pilot episode).
When ComicBook.com reached out to Marc Guggenheim, Arrow executive producer, for clarification, he was tantalizingly non-committal. And while neither he nor the network have said anything further to imply that the glimpse fans got of the back of Alexa's head could be a hint that Harley is coming to Starling City, Alexa herself seems to be enjoying the speculation.
Her agency, reached by Comic Book Therapy, confirmed that was Alexa in the teaser, but couldn't confirm anything about the role, which is being kept secret even from them. They also referred to the appearance as a "cameo," leaving some to wonder whether we'll see any more of Alexa in the episode than we did in the trailer.
"Cassidy Alexa is getting a lot of heat surrounding her upcoming ‘cameo’ on Arrow," said Andrew Webster, Head of Talent for Webster Talent. "I’m in the dark as to what the producers have planned for her so we’ll have to find out. She’s a very exciting young actress to keep an eye on."
When rumors of a live-action Suicide Squad movie started to float around last year, it was widely assumed that Harley would play a role, since the character had been the face of the most recent incarnation of the comic book series starring the team.
When the Squad turned up on Arrow, though, assumptions turned the other way; not only has The CW had a hard time historically convincing DC Entertainment and their mutual parent company Warner Bros. to allow them to use Batman characters (not just in Arrow but famously on Smallville as well), but Fox is moving forward right now with Gotham, a Zero Year-style retelling of the city's slow descent into super-crime immediately prior to the appearance of Batman. With that show on the air, many reasoned, we wouldn't see anybody visiting from Gotham City on Arrow, lest it cause some friction with Fox.
If indeed it's implied that this character is Harley Quinn, but Alexa doesn't play a major role in the episode, it's not outside of the realm of possibility that a potential Harley appearance down the line could be recast. Early in the casting process for the show, Birds of Prey star Ashley Scott took to Twitter to let fans know she was auditioning to play Kate Spencer, a character who in the comics would go on to become the vigilante Manhunter. Scott's tweet went viral online, but the actress never got the part (it went to Chelah Horsdal). Since Alexa has already appeared onscreen, though, the more apt comparison might be to Jacqueline MacInnes Wood, who played Sara Lance during a few flashbacks in the first season but who was replaced by Caity Lotz when the character became a series regular this season.