While the reviews for Suicide Squad were mostly mixed to negative, one thing that most critics agreed was good about the film was Margot Robbie's Harley Quinn. While Harley was always a popular character, Robbie's portrayal was good enough to convince Warner Bros. that a solo Harley Quinn should be greenlit for production.

Now that the Harley Quinn movie is moving forward, the question now is - what is the film actually going to be about? Will we have a film starring Harley as a villain protagonist who goes around causing crimes? Will Harley be forced into undertaking missions for the government like in Suicide Squad? Has the popularity of the character convinced studio executives that Harley should do a heel-face turn, and become a hero?

No matter what the movie is about, the age old rule of storytelling still applies - any story worth telling requires conflict. Harley is going to need an opponent in her movie, and she has a wide variety of heroes and villains who would want to take her down. From the numerous members of the Bat family who want to see her behind bars, to the many fellow criminals who can't let go of a grudge, here are 15 Villains Harley Quinn Might Face In Her Solo Movie.

15. Batman

All-Star Batman DC Rebirth Best Comics

When you consider that Harley Quinn first appeared in Batman: The Animated Series as the Joker's chief henchwoman, it seems that the most likely candidate to face Harley in her own movie would be the Dark Knight himself.

While Batman might seem the obvious choice as the antagonist of the Harley Quinn movie, there are several factors working against it. We already know Batman is showing up in Justice Leagueand that a Batman solo movie is in the works. Due to us not knowing the specifics of Ben Affleck's contract with Warner Bros., we do not know how many movies he has signed on for. He has already used up at least three of his contractual appearances. If the next few DC movies are financial and critical failures, then he may want to jump ship as soon as possible. Using him in the Harley Quinn film may seem like a waste, when there are so many other potential foes for her to face.

The idea of Batman being the villain in Harley Quinn is not completely out of the realm of possibility. In the slew of bad reviews that followed Batman v Superman and Suicide Squad, two of the most highly regarded performances from those films were Ben Affleck's and Margot Robbie's. Warner Bros. might be so desperate for a hit, that they would put their two most popular characters together.

14. Poison Ivy

Gotham season 3 casts Poison Ivy

Outside of Batman and the Joker, the character who is most associated with Harley Quinn is Poison Ivy. The two of them have been criminal partners since the days of Batman: The Animated Series, and later portrayals have shown them as being more than just friends (a fact confirmed by DC).

Poison Ivy's powers have been depicted in many different ways throughout the years, so it is difficult to pin down how she would exactly match up in a fight against Harley. Some writers have given her the ability to control nature and create plant monsters (as seen in the Arkham video game series), whilst others have presented her with power over pheromones (like the Purple Man), that allow her to control people (as in Batman and Robin). A mixture of these powers could make for an interesting antagonist.

The big question is whether a romantic relationship between the two would be possible? The issue isn't about former enemies becoming lovers, but the fact that it is two women. Even the Marvel Cinematic Universe, with its numerous films & TV shows, has yet to include an LGBT character in a leading role. Are Warner Bros. really progressive enough to present a relationship between two bisexual women on the big screen that isn't just there for titillation?

If the producers of the film are unwilling to present a romantic relationship between the two, then perhaps establishing them as villains is a way to sidestep the issue without offending anyone.

13. Catwoman

Catwoman New 52 Batman Greatest Comic Villains

Catwoman has something of a bad rap when it comes to movies. The Catwoman solo film from 2004 was a box office bomb that was savaged by critics. The film won seven Golden Raspberry awards, and Halle Berry actually showed up to accept them, calling the film a "piece of sh*t, godawful movie". The hatred for the Catwoman film seems to have soured audiences on the character, to the point where even Michelle Pfieffer's memorable performance from Batman Returns seems to have been forgotten.

If DC wanted a way to return Catwoman to the movies, then making her the villain in the Harley Quinn film is a safe way to do it. They are similar enough to make good opponents, but different enough that they would interesting foils for the other. Rather than being straight up antagonists, the premise of the film could be about a competition between villains to see who can commit a specific crime first. If Warner Bros. intention is to make the films more lighthearted going forwards, then a rivalry plot might be more palatable than two criminals trying to outright murder each other.

12. Zatanna

Zatanna from DC Comics

Zatanna is a superheroine with powerful magic abilities, that are based around spells that have to be spoken backwards. If Batman is charging at her, all she needs to say is "Namtab Pots", and he will be frozen where he stands. On top of the interesting way in which she implements her powers, Zatanna also dresses like an alluring stage magician, making her a very popular character.

Even though she is primarily an associate of the Justice League, Zatanna is regular recurring character in many Batman comics. Despite her magical powers (that some would say are overpowered), writers love mixing Zatanna with the criminal underworld of Gotham City. This means that she has crossed over with Harley on many occasions in the past. While Zatanna is powerful, her magic is based around her voice, and will not work if she cannot speak or her opponent cannot hear her. This gives Zatanna a major exploitable weakness for a canny foe like Harley to use against her.

There have been attempts in the past to make a live action Zatanna movie that have never materialised. Her inclusion in the Harley Quinn film may finally be a way for DC to drum up enough interest for a solo movie.

11. Nightwing

DC Rebirth Nightwing

From what we have learnt so far in Batman v Superman and Suicide Squad, Batman has had at least one Robin for a sidekick, who would later go on to be murdered by the Joker and Harley.

Just because one Robin was killed in the past, that doesn't mean there weren't others before him...

Nightwing is the grown up version of Dick Grayson, the original Robin. Once he had outgrown the tights and hand-me-down gadgets, he would go on to form a new secret identity and become the protector of the city of Blüdhaven. Nightwing shares his time between the numerous Batman series, the Teen Titansand his own solo comic. As such, he is a prolific and popular character among the fanbase.

If using up another of Ben Affleck's Batman appearances is off the table, then Nightwing could be a good substitute. He is similar to Batman in terms of abilities and has fought Harley across several mediums (such as the comics, the Arkham video games, and Batman: The Animated Series). The only issue would be explaining his absence in the other films to date (which could be easily handwaved away.)

10. The Joker

Joker and Harley Quinn in Arkham

The problem with portraying an iconic comic character in a movie is that you will always be unfairly compared to your predecessors. Comic book movies may be the genre that is easiest to reboot, due to the sheer wealth of source material to draw from. This means that you are more likely to see many different actors portraying the same iconic character across several big budget films over the years.

When it comes to the latest iteration of the Joker, the new actor taking the role would be facing way more scrutiny than usual. This is due to Heath Ledger's incredibly performance in The Dark Knight, along with his tragic death sealing his place in the memories of the audience.

Jared Leto was the man who put his career on the line by becoming the next Joker, and the reception was... not great. The critical and audience reaction was mixed to say the least, and it has been suggested by many fans that he should be replaced.

Whether Jared Leto's performance was hamstrung by executive meddling, the lingering memory of Heath Ledger, or just plain old bad acting, there still exists an opportunity to redeem the character. With Batman busy in Justice League, a story about Harley breaking away from the Joker could give both characters enough screen time for the audience to appreciate the new Clown Prince of Crime.

9 . Supergirl

Supergirl Kara El-Zor Strongest Superhero

The original Supergirl was killed during the events of Crisis on Infinite Earths. Once that series ended, the DC comics universe underwent the first of many reboots. When Superman's new origin was laid out, the editors decided that he should be the only surviving Kryptonian. This meant that several characters would not be returning, such as Krypto the Superdog, and Supergirl.

There were several attempts by different writers over the years to bring Supergirl back. In 2004, Jeph Loeb finally succeeded in the pages of Superman/Batman. After Supergirl returned to continuity, one of her first fights was against Harley Quinn & Poison Ivy.

In terms of power, Supergirl outshines Harley in every sense, and would easily squash her in a fair fight. That being said, Harley Quinn is a villain, and any fight with her is not likely to be fair. After the events of Batman v Supeman, the Kryptonian weakness to Kryptonite will have become public knowledge (especially among supervillains). A Harley vs Supergirl film could go on to be the distaff counterpart to Batman v Superman.

With Superman's resurrection confirmed (with the announcement of a sequel to Man of Steel), the arrival of Supergirl with a slew of Kryptonian technology may be the method by which he is returned to life.

8. Static Shock

Static Shock

To those who are only barely familiar with the cartoon Static Shockit may be surprising to learn that it was an official part of the DC Animated Universe. Throughout the run of the series, Static Shock crossed over with Batman: The Animated Series, Superman: The Animated Series, and Justice League. An older version of Static would show up in episodes of Justice League Unlimited, where he is portrayed as a member of the Justice League during the Batman Beyond era.

It was during one of the crossovers with Batman: The Animated Series that Static fought against Harley Quinn and Poison Ivy. In terms of powers, he is a mixture of Magneto and Electro. He is actually very powerful, but has numerous weaknesses due to the nature of his abilities. Static's powers are based around electromagnetism, and while this may sound powerful, he can be defeated by insulation. Anything that prevents the conduction of electricity prevents his powers from working. This could make him a credible threat to Harley, whilst still being beatable enough to make her victory seem realistic.

Static's inclusion in the film could be an attempt by DC/Warner Bros. to emulate what Marvel did with Black Panther in Captain America: Civil War. By giving him a major role in someone else's movie, the positive or negative reaction of the audience can be judged without the financial risk of giving him his own film.

7. Thorn

Rose and Thorn

While not as well-known as the other characters on this list, Thorn may be the closest thing to a "heroic Harley Quinn" style of character, which is odd, as she was created in the 1970's.

Thorn (real name Rose Forest) is a woman in her mid-twenties who suffers from multiple-personality disorder. In a manner similar to Legion from the X-Men comics (another character she predates), one of Thorn's personalities is a heroic vigilante. Thorn was the daughter of a Metropolis City police officer, who was murdered by a street gang called The 100. When Rose falls asleep, her "Thorn" personality takes over, and she becomes a costumed hero. Thorn's goal is to see The 100 brought to justice, as revenge for her father.

In terms of strength, Thorn is only skilled at hand to hand combat, and lacks any sort of superpower. She would be Harley's equivalent in terms of  fighting ability. Thorn could also be interpreted as a heroic version of Harley. Both of them were driven mad by the actions of criminals, which dragged them into the world of masked vigilantes and superheroes. Whilst Harley's madness made her into a homicidal maniac, Thorn's turned her into a force for good.

6. The Secret Six

The Secret Six

At the end of 2005, DC began a company-wide crossover called Infinite Crisis. Alongside the main issues of this series, there were four other miniseries that tied all of the different story elements together. One of these was called Villains United. During Infinite Crisis, an impostor posing as Lex Luthor gathered an army of supervillains together under his control. It is up to the real Lex Luthor to gather his own team of villains to work on his behalf. This team was known as the Secret Six, and their adventures in Villains United were popular enough to give them several follow-up series.

There have been numerous different members of the Secret Six over their run, but a few of most likely candidates to show up in Harley Quinn are - Catman (a self-admitted lesser copy of Batman), Cheshire (imagine Catwoman if she used poison weapons), Scandal (the daughter of the immortal villain Vandal Savage), Knockout (a super-powered former soldier of Darkseid), and The Fiddler (a Flash villain with music based powers).

The one member of the Secret Six who holds an established rivalry with Harley in the comics is Ragdoll. Originally a villain of the Golden Age Flash, Ragdoll is a master contortionist, who underwent numerous surgeries in order to make himself as flexible as possible.

So why does Ragdoll hate Harley? He thinks her costume looks too much like his own.

5. Batwoman

Batwoman DC Comics

One of the new heroes who showed up in during the DC comics 52 event was Batwoman. Katherine Kane is a wealthy socialite who uses her money and resources to fight crime. She donned the mantle of Batwoman, and became the protector of Gotham City in Batman's absence following Infinite Crisis.

Despite the name, the modern incarnation of Batwoman is not as linked to Batman as the other members of the Bat family. Her inclusion in the Harley Quinn film would come without the backstory baggage of someone like Nightwing.

Even though Batwoman seems like she may be the perfect fit for this movie, there is one huge potential issue with her inclusion. In the comics, Batwoman is a lesbian, and is probably the most high profile gay superhero in the world today. It is sad to think that in this day and age, Warner Bros. would be nervous about the inclusion of a homosexual lead character in a superhero movie. If Batwoman was a lesbian like she is in the comics, then the usual gangs of anti-gay groups would be boycotting the film. If her sexual preference was changed, then gay fans & their supporters would do the same. It is more likely that Warner Bros. would just not bother with the character at all.

4. The Birds of Prey

Birds-Of-Prey

The Birds of Prey are a team of all-female superheroes. The most well-known lineup of the group included Black Canary, The Huntress, and The Oracle. All of these characters have tangled with Harley in the comics (both individually and as a group), and any one of them would make a strong contender as the villain for a Harley Quinn film.

Black Canary is a martial arts based superhero, who has one super power (a sonic scream that can deafen and damage opponents). In recent years, she famously fought Harley in the pages of Injustice: Gods Among Us: Year Two, where Harley revealed that she gave birth to the Joker's child.

The Huntress is a masked vigilante who hunts down members of the Mafia. Unlike most of her contemporaries in the Bat family, Huntress has no problem with killing her foes (a fact which got her kicked out of the Justice League).

The Oracle is Batgirl after she is crippled by the Joker during the events of The Killing Joke. It is more likely that they would introduce her as Batgirl first, rather than as a character with so much established backstory.

There is one last piece of potential evidence that Harley will face the Birds of Prey on the screen - it has happened before. In 2002, The WB network produced a TV show based on the Birds of Prey. Harley Quinn appeared as a villain in 13 episodes of the series.

3. Robin/Red Hood

Jason Todd as Red Hood, with guns pointed at the screen

It has been pointed out that a message flashes up during Suicide Squad that confirms the death of Robin. During Harley's introduction, text flashes on screen saying "accomplice to the murder of Robin."

There have been many different Robins over the years, but the identity of the dead one is most likely Jason Todd. Jason was the second person to take up the mantle of Robin, and he was not as well liked by the fans as his predecessor. In 1988, DC ran a storyline called "Batman: A Death in the Family", where readers got to vote on whether Robin lived or died. They voted for him to die...

Jason Todd was killed by the Joker, and a new Robin (Tim Drake) would go on to take the mantle.

In recent years, Jason Todd has become famous for refusing to stay dead. He was resurrected during the Under the Hood event of 2005, and would become the vicious vigilante known as the Red Hood. He would also have a similar revival in Batman: Arkham Knight, where he was revealed to be the Arkham Knight that was attempting to kill Batman.

If Jason Todd returned as the Red Hood, then wanting revenge against the woman who had a part in his attempted murder would give him a very good reason to be the villain in Harley Quinn.

2. No One At All...

Dr-Harleen-Quinzell

As we only got a brief glimpse of Dr. Harleen Quinzel in Suicide Squad, the Harley Quinn movie may actually be a more comprehensive telling of her origin story.

One of the big criticisms of Suicide Squad involved the pacing at the beginning to the movie, as a large chuck of the intro had to go towards setting up all of the characters. Since the release of the film, many news reports and articles have talked about the behind the scenes turmoil that influenced the final edit of Suicide Squad. If these reports are to be believed, then Warner Bros. seem to be very reactionary in how they deal with issues. The audience complained about Superman Returns not having enough action? Let's fill Man of Steel with Dragon Ball Z style fight scenes. Reviewers complained about the grim atmosphere of Batman v Superman? Let's spend millions on reshoots for Suicide Squad to add more comedy, and release a trailer for Justice League that makes it look like a wacky screwball comedy.

With people complaining about the lack of origin story in Suicide Squad (which wasn't helped by using mostly obscure characters), Warner Bros. might go for a film that focuses on Harley's descent into madness whilst working at Arkham Asylum. With the final scene showing her being introduced to the Joker for the first time.

1. Batgirl

Batgirl Silver Age Killing Joke Animated

When Harley Quinn became the breakout star of Batman: The Animated Series, the character was placed in the unusual position of being a high profile female villain in a cartoon whose lead was a male. This meant that Batman couldn't exactly beat the crap out of Harley, in the same way that he would with other villains.

There was one character who could, and often would fight against Harley, and her name was Batgirl.

Barbara Gordon was the daughter of Police Commissioner Gordon. She would become another of Batman's teenage sidekicks, and prove herself to be one of the greatest crime fighters of the Bat Family. She has been one of the chief rivals of Harley Quinn throughout most mediums, and was even believed to have killed her during the events of Batman Beyond: Return of the Joker. Harley falls from a cliff whilst fighting Batgirl and is thought to have died (although it is revealed at the end of the movie that she survived).

With DC/Warner Bros. receiving criticism from fans about the addition of sex scenes between Batgirl and Batman in the animated adaption of Batman: The Killing Jokea leading role in Harley Quinn may be their way of making amends for what was considered a sexist portrayal of the character. Batgirl and Harley Quinn have been enemies from the start, and there could be no better way to continue that feud than on the big screen.