Warner Bros is developing a spin-off for "Suicide Squad" starring Harley Quinn, and they're calling it "Gotham City Sirens." "Sirens" will star Margot Robbie as the psychotic Harley Quinn, who will also executive produce. On December 13, director David Ayer tweeted news that seemed to indicate the movie will also feature Catwoman and Poison Ivy. The title "Gotham City Sirens" was the name of a comic book series that ran from 2009 to 2011, and focused on the three villains working together in the streets of Gotham.

RELATED: Gotham City Sirens Taps Suicide Squad’s Ayer to Direct

We don't know for sure how heavily the movie will be based on the comic books, but we do know what we're looking for on the big screen. Here, then, is CBR's list of 15 things we hope to see in the upcoming "Gotham City Sirens" film.

15 Harley and Poison Ivy

In "Gotham City Sirens," we'll see Harley Quinn and Poison Ivy together on the big screen, and they'll most likely become fast friends. The relationship between Harley and Ivy goes back a long time, both in comics and on the small screen. In 1993, "Batman: The Animated Series" aired "Harley & Ivy," where the two team up and go on a crime spree. Since then, their partnership became an integral part of the Batman universe, whatever the medium.

While their friendship in "Sirens" is probably a given, some fans have wanted it to become something more. Many fans, both identifying with the LGBTQ community and not, have long wanted to see the two in an open romantic relationship in the comics. This goal was achieved in the alternate universe "Bombshells" #42 (2015), wherein Harley and Ivy shared a passionate kiss. The same call has already gone out among fans to see their romance appear in "Sirens," which would obviously be a huge step towards diversity, but also an incredible point in the narrative.

14 Wonder Women

For the most part, superhero movies haven't been kind to the female audience. The few heroes who have appeared on-screen, like Black Widow, have been mostly in the background, or mired in overwrought narrative complexity. While this is changing with movies like "Wonder Woman" and "Captain Marvel" slated for 2017, "Gotham City Sirens" could appeal to women more than any other comic film in history.

This movie could feature three (or more) lead female characters as its main leads, which means it could pass the Bechdel test with flying colors. For a movie to pass the Bechdel test, it needs to feature at least two women who talk to each other about something other than a man, and is considered by many to be a benchmark for a realistic portrayal of women. But, as always, the Bechdel Test is just a start. With Harley Quinn, Catwoman and Poison Ivy all in the same film, it's likely they'll have other things to talk about than Batman and the Joker. More importantly, "Sirens" could also be a chance to show a true relationship among super-powered women with agency and purpose, not to mention showcasing how each kicks butt! That's something everyone would enjoy.

13 Gotham City

In movies like "The Dark Knight," we've mostly seen Gotham City from the perspective of Batman or its villains: a dark and menacing world full of psychotic characters stealing and murdering, with a man dressed as a giant bat to stop them. Bruce Wayne's stately manor is usually the house we spend the most time in and around, and the streets are full of random people screaming and running. In the TV show "Gotham," we've seen more of the city, but in "Gotham City Sirens," we could see it from a brand new and much-needed fresh perspective.

Gotham is obviously full of people living and working under the shadows of Batman, one in which the Sirens would live. In "Sirens," we could see what life is like in Gotham for the average Joe and Jane. In the comic book "Gotham City Sirens," Catwoman had to deal with finding somewhere to live, Harley went shopping and all three went on vacation. In their encounters, the movie would show a city in fear, but living their lives would be paramount to understanding their individual characters, and shine a harsh light on what it is Batman is so furiously protecting. Maybe we'd see scenes of people talking about the latest Batman sighting or buying superhero insurance. This film has the chance to make Gotham City more real, and it would be a wasted opportunity not to.

12 Harley and Joker

Any story involving Harley Quinn is going to have to explore her relationship with "Mistah J." We got to see some of it in "Suicide Squad," but, as the sometimes angry fan reaction suggested, there's a lot more ground to cover. In the comics, Joker and Harley have a twisted romance when they are together, with the Joker often exploiting her until she leaves him to strike out on her own. Once she's away from him, the Joker convinces her to come back, and the cycle continues in what is, essentially, a harsh light on an abusive relationship. The "Sirens" series featured a similar arc where Harley rebels from the Joker, but comes back to free him from Arkham Asylum (well, she frees someone who she thinks is the Joker).

It would be great to start "Sirens" in the same arc, with her rebelling from the Joker and facing the prospect of being free of his control, while struggling against the desire to return to him. This could also become an interesting love triangle between the Joker, Poison Ivy and Harley Quinn. Just sayin'.

11 Batman and Catwoman

Batman and Catwoman have a rocky relationship. Catwoman has her own agenda, where she commits crimes or helps the weak, depending on how she feels at the time and whether it suits her interests. That means sometimes she's an ally of Batman, and other times she'll fight against him. Still others, they just start making out -- or more -- on rooftops. Their mutual attraction has been a massive part of the comics, a big part of the movie "Batman Returns," and it should be in "Sirens."

In fact, with "Gotham City Sirens," we could explore that relationship in more detail. With the focus on Catwoman, we could see it from her perspective for once; how she pursues her goals and tries to manipulate and seduce Batman to her own ends. We'd also like to see her talking about her feelings for Batman with Poison Ivy and Harley. We don't want the whole movie to feel like a soap opera, of course, because "Sirens" shouldn't just be about romance, but it could deal with the practicalities and pitfalls of their love story better than other superhero movies, and even many of the comics!

10 The Bat

Wherever there's Harley Quinn, Poison Ivy and Catwoman, we would expect to find Batman, especially since the movie is set in Gotham City. Ben Affleck made a cameo as Batman in "Suicide Squad," and it would almost be impossible to do "Sirens" without having at least a brief mention or appearance of Batman.

Since the trio of villains would most likely be doing some sort of crime in "Sirens," we expect Batman to be trying to stop them (or at very least one of his surrogates, like Nightwing). They all have history with the Caped Crusader, and would be trying to avoid him. It wouldn't have to be a huge role in the movie, of course. In the original "Gotham City Sirens" trilogy, Batman was mentioned a lot, but rarely appeared. The movie could be the same, where we hear about him and feel his presence, but his shadow looms large. We would want to keep the focus on the three villainous ladies, but it would be hard not to bring in the Bat.

9 The Man Who Laughs

While it may be debated across the internet, we here at CBR think Jared Leto did a tremendous job as the Joker in "Suicide Squad." However, one of the biggest complaints of the movie is that he wasn't in it enough. His appearance, for better or worse, was really just an extended cameo, such that even Leto himself complained that so many of his scenes were cut. With "Gotham City Sirens," there would be a chance to showcase Leto's performance and make his Joker all the more robust.

In a movie focused on Harley, it would be impossible to talk about her without getting into her mentor. In the original comic series, Harley spent an entire story arc trying to free the Joker, and as we've discussed, that could certainly happen in the "Sirens" movie. Alternatively, the Joker could be trying to get to Harley to bring him back into his organization. More than anything, it would be a chance to watch Leto chew up more screen time with those metal grills of his. And for our money, with a personality as large as the Joker's, that's always a good thing.

8 Poison Ivy Done Right

Once again, we have to look to the abominable "Batman and Robin" from 1997 to see a movie where Poison Ivy was given any screen time. We have to admit, though, as many others also thought... that movie was pret-ty terrible. Uma Thurman played Ivy as a Mae West-type vamp who made bad puns, wore outrageous hair-dos and popped out of giant flowers. With "Sirens," we could have a Poison Ivy finally done right.

Ivy is a calculating villain in the comics with an ethereal beauty and pheromones that can control men's minds. "Sirens" could show her in all her glory, starting with a recap of her origin as a scientist who was injected with an experimental serum, turning her toxic. With her control of plants, she could be an elemental force of destruction in Gotham City. She also has a strong theme of eco-terrorism, which could be very topical in the "War on Terror" and "Global Warming" era in which we live. In the "Sirens" comic series, she showed a more tender side as she teamed up with Catwoman and Harley to protect them; the movie could do the same, and in so doing, give some much-needed dynamism to the Ivy character.

7 Catwoman Done Right

Catwoman has been treated pretty well in the movies and on TV, but there's still room for her to be done right. Her first movie appearance, outside of a made-for-TV movie pegged to 1966's "Batman" TV show, was in 1992's "Batman Returns," which portrayed her as a sort of zombie dominatrix who died, was brought back to life by cats and squeezed into a leather outfit to straddle Batman. The less said about Halle Berry's 2004 film, the better. Even Anne Hathaway's performance as Catwoman in 2012's "The Dark Knight Rises" wasn't the version we know from the comics, and while more in-depth, wasn't universally beloved by fans. She didn't even technically call herself Catwoman.

In "Sirens," we hope Catwoman will be the confident and morally ambiguous woman we've loved in the comics. We'd love to see her flying over rooftops with her whip, dazzling with martial arts and kicks, and then returning home in time to cuddle with her feline friends. At the same time, there's a tragic element to Catwoman that's always been pulsating under her surface, and we hope to see that brought more to the fore to make her a solid presence and a more relatable character in the movie.

6 Strong Story, Strong Villains

The biggest question about "Gotham City Sirens" is, of course, what the movie will be about. With three villains as the main characters, we could expect some kind of crime movie. The storyline could involve Catwoman, Harley and Ivy teaming up when they discover they're all after the same treasure. It could be a stealthy heist film, like 1996's "Mission Impossible," with Catwoman dangling from wires. Or it could be a wild chase heist in the vein of the "Fast and Furious" series.

In order to make the trio anti-heroes, they should go up against a major, more villainous threat. In the "Gotham City Sirens" comic series, one of their major enemies was Hush. A brilliant surgeon, Hush altered himself to look like Bruce Wayne, and fooled the Sirens into thinking he was Wayne to infiltrate their group. That could certainly be a story in the movie, and would also tie into Batman appearing in the film, with the extra bonus of setting Hush up as a character for a standalone Batman movie later. The Riddler was another recurring character in the comic book series, we would love to see mix it up in "Sirens."

5 Suicide Squad 2.0

When "Suicide Squad" came to theaters, there was a great deal of excitement and anticipation. Comic book fans and moviegoers alike looked forward to it as an antidote to what had become a formulaic presentation of comic book movies, like the ongoing "Avengers" franchise, Instead of a movie about square-jawed heroes fighting dastardly monsters with a sober and emotional tone, "Suicide Squad" promised to be about supervillains forced to do the right thing, fighting other villains who were worse than them. There was also a lively and fun tone to the trailer that fans expected to find in the movie. Unfortunately, instead, viewers found a confusing and depressing movie that didn't deliver much of what it promised.

"Gotham City Sirens" could be the second take on "Suicide Squad" fans were hoping for, and present the film they were hoping to see. It's also about a group of supervillains, but with only three characters, the movie will have time to develop them properly. It also wouldn't have the "suicide" aspect to deal with, freeing it to be a fun movie where no one necessarily has to be killed.

4 Lighten Up

If the movie is truly based on the "Sirens" comic book, it would be a refreshing change from the usual dreary tone of DC movies. "Man of Steel" and "Batman v Superman" were both somber movies shot in shades of gray, dripping with morality and misery. Similarly, "Suicide Squad" was a brutal and hardcore bloodbath. While "Justice League" is promising to be lighter, it would be like a drama compared to "Gotham City Sirens."

The comic series, initially written by Paul Dini, was a bubbly and fun comic book that emphasized comedy and zaniness more than drama. Harley, Catwoman and Ivy were opposites in many ways, which led to a lot of bickering and arguing, but also laughing and camaraderie. They were less concerned about fighting and killing superheroes than they were finding a steady income and hanging out with each other. Even villains like the Riddler ended up as punchlines more than threats. We want a lighter and funnier movie from DC, and "Sirens" could deliver, thus striking a new tone for the DC movies and actually getting a new audience of viewers who are otherwise turned off by the so-called "DC Murderverse."

3 Birds of Prey

What would really take the feminine -- and feminist -- approach to a new level would be to put the Sirens up against the Birds of Prey. "Birds of Prey" began as a one-shot comic in 1995 featuring Black Canary and Barbara Gordon as the computer hacker Oracle. Over time, the Birds of Prey came to be a combination of Black Canary, Oracle and the Huntress. Other female superheroes came to join the team, and at one point even Catwoman and Poison Ivy worked with the Birds of Prey, establishing the group not just as a legacy, but as a multi-media success.

Earlier in 2016, it was announced that Warner Bros was developing a movie based on "Birds of Prey," but the project was cancelled in favor of "Gotham City Sirens." The work developing "Prey" could easily be incorporated into "Sirens," where it could give the project and title agency to flourish as its own property. In "Gotham City Sirens," the Birds of Prey should be the main heroes after the Sirens, with Batman taking a backseat. Later in the movie, the teams could fight and/or team up together to fight a greater threat.

2 Oracle

If Barbara Gordon did make an appearance, it could be tied into her storyline from the 1988 graphic novel "The Killing Joke." Gordon originally began as Batgirl until "Killing Joke," when the Joker shot and paralyzed her in an attempt to drive her father insane. With her confined to a wheelchair, Gordon developed an advanced computer network and used her skills at hacking to assist superheroes in fighting crime as Oracle, arguably the most popular version the character, even beyond Batgirl. She became a new kind of hero, and physically challenged communities praised the character for her strength. The problematic nature of her paralysis notwithstanding, her evolution into the Oracle role is an iconic storyline that could be awesome to see on the big screen.

Her journey could be a major part of "Sirens," where Gordon starts the movie as Batgirl, along with the other Birds of Prey. She could be injured by the Joker in a moment of crisis or, perhaps even better, harmed in the line of duty, protecting innocent lives. In the end, she could become Oracle. Of course, Gordon could return to full health in the sequel, like she has in the comics (even though many fans also have a problem with that retcon); but either way, it would be both great and important to see Oracle on the big screen.

1 The Casting

As far as the cast, we already know Margot Robbie will reprise her role as Harley Quinn. But who will play Poison Ivy and Catwoman is a speculative exercise that remains up in the air. Us being us, though, we do have some picks!

For Poison Ivy, rumors are swirling that Megan Fox will be offered the role, but we think Jessica Chastain would be a much better pick. She's an incredible talent to start, and one who could embody Ivy's imposing physical characteristics beautifully. She has also expressed interest in playing a supervillain. Scarlett Johansson would be another great choice if she's willing to make the leap from the Marvel Universe to the DC Universe, but we won't hold our breath for that anytime soon.

As for Catwoman, Eva Green is at the top of our list of candidates. She has the dark hair and sultry wiles innate in her onscreen performance, not to mention the dramatic skills to make Catwoman a tragic and intelligent villain. As a second choice, an African-American actor like Kerry Washington could add diversity to a role that already has history with it, thanks of course to the late, great Eartha Kitt. No matter who they pick, though, we're looking forward to seeing these bad girls in action, and will be the first in line to see "Gotham City Sirens" when it hits the big screen!

What are you looking forward to in "Gotham City Sirens?" Let us know in the comments!