Harley Quinn appears to be of one of a few character Warner Bros.' is trusting to ensure the success of its DC Extended Universe. The popular DC Comics character is currently slated to appear in four future movies: the Suicide Squad sequel from Gavin O'Connor, Gotham City Sirens directed by David Ayer, a Joker and Harley Quinn romantic comedy from Glenn Ficarra and John Requa, and the newly-confirmed standalone Harley Quinn flick.
The latter of the bunch was revealed by Suicide Squad actor Margot Robbie just a few days ago, but the only pieces of information she'd divulge was that it's completely separate to any movie that's been announced so far, and that she's been working on the movie - in which she'll act as star and producer - for two years. So, since there's no lead on just what the solo Harley Quinn film will explore, let's take a look at some moments from DC Comics that need to appear!
Batman Adventures: Mad Love
First things first - it's easy to forget that Harley Quinn has only appeared in live-action once so far, especially with all of the other projects that are in development. Suicide Squad was Harleen Quinzel's introduction to the DC Extended Universe but her origin didn't receive much attention, which makes sense considering the movie is an ensemble piece with a handful of main characters.
So, following Batman Adventures: Mad Love - a one-shot comic published 1994 - her solo movie should properly establish her origin story so movie-goers can get a really good understanding about why she turns into a villain and just how infatuated she is with the Joker. This'll allow the Joker & Harley Quinn movie to do something beyond fleshing out their toxic relationship.
This comic tears Harley away from the Joker, giving her time to shine on her own and giving fans a break from watching her pine over him. If they want a strong leading lady, then she needs to be able to operate on her own away from a male lead - just look at Wonder Woman. Yes, Diana falls in love with Steve, but it doesn't stop her from getting the job done.
Harley Quinn: Preludes And Knock Knock Jokes
Harley Quinn and the Joker are practically synonymous with each other, which makes complete sense as there'd be no Harley without her puddin'. With that being said, their close relationship means there are not many standalone stories focusing on her, but one solo series that the movie could take inspiration from is Harley Quinn: Preludes and Knock Knock Jokes.
Collecting issues #1 to #7 of her solo run, this story was published in 2008 and kept the lighthearted, fun tone of Batman: The Animated Series. Of course, violent and crazed villains can only be so light in tone before it gets ridiculous, but this story balanced it perfectly.
Gives Harley purpose beyond Joker. She may need a break from him since they're set to appear in multiple movies together. Harley rescues the Joker from Arkham Aslyum but by the end of the first part of the story, she's all alone - this is something that could be adapted in the film as a way to honor their relationship while giving her some much-needed alone time.