It is easy to underestimate Harley Quinn, if one does not know too much about her. Despite appearances, Harley Quinn has been able to go up against (and defeat) powerful opponents like Lobo, Black Canary, and even Superman. One of her most defining traits is her unpredictability, something she often utilizes to her advantage against stronger opponents.
Combined with her intelligence, peak athleticism, and enhanced strength, agility, and reflexes (via Poison Ivy's serum), Harley's fought and won her fair share of battles. That being said, there have always been a select number of opponents who've proven too much for her, on both physical and physiological levels.
10 The Joker Always Messes With Harley
Being part of her origin, it's only natural that The Joker is often involved with large amounts of Harley's story. Though she has since broken away from him in more recent years, his presence often unhinges Harley to the point where she either goes ballistic on him or she defects back to his side.
While Joker doesn't "win" in the traditional sense, he does disrupt her process of recovery, in almost all mediums the two appear together. It's true that Harley is a far different person and character than her debut, but Joker does his best to remind her exactly how much control he once had over her.
9 Granny Goodness Isn't A New God For Nothing
Leader of the Female Furies and one of Darkseid's most notable lieutenants, Granny Goodness has her position for a reason. Every bit as calculating as her master (though arguably far crueler), her training methods are sadistic and brutal, and has been the mentor to several DC powerhouses, including Big Barda, Knockout, Stompa, & Lashina.
In Harley Quinn #45, Goodness wanted Harley to become a fury, and though she was successful, Harley began to have her doubts when the inhabitants of Apokolips reacted to her status with fear. Gaining a new ally in the former fury Petite Tina, Harley was able to return to Earth, but not before Goodness beat Harley to a pulp. Harley failed to best Goodness in combat in her titular show as well, only winning after Doctor Psycho began controlling her unconscious body.
8 Batman's Superior Skills Save His Skin
As a former member of Batman's rogue gallery, it's no surprise that Harley has clashed with Gotham's caped crusader countless times over the years. Whether she was fighting alongside Joker, Poison Ivy, as a member of the Suicide Squad, or just by herself, Harley has had plenty of time to best Batman.
Granted, there have been several situations where Harley has outsmarted him, most notably during the Heroes in Crisis storyline and in Batman: The Animated Series. Still, Batman always finds his footing, either by making Harley see the error of her ways, escaping the situations she puts him in, or by besting her in combat.
7 Wonder Woman Has Only Briefly Faltered Against Harley
Largely hailed as one of the most powerful heroes in DC's universe, Wonder Woman is an ageless and powerful Amazon Warrior, and the only female member of DC's "Trinity" - composed of Wonder Woman, Batman, and Superman. Trained from a young age in the art of combat and outfitted with her Lasso of Truth and indestructible bracelets, Wonder Woman has often been dubbed unstoppable.
Wonder Woman usually doesn't have any problem against opponents like Harley - most notably in the Injustice universe - but she has been taken by surprise a few times, such as when Harley took Wonder Woman out with knockout gas or when Harley stole the Lasso of Truth in Heroes in a Crisis. Nevertheless, Wonder Woman has always come out on top or without sustaining any real damage.
6 Punchline Throws Harley's Sympathy Back In Her Face
Following Harley's defection from Joker, Punchline became his new right hand and "paramour." Born Alexis Kaye, she became infatuated with Joker during her time in college, meeting him through the internet. Unlike Harley, Punchline claims that what she and Joker have "is real," and that she loves Joker for his "intellect." When she and Harley first met, they briefly sized each other up, quickly resorting to violence (as Harley had allied herself with Batman).
It seemed that Harley held back out of sympathy at first, something Punchline took full advantage of, winning the fight by slicing open Quinn's throat. After stitching her wound with a guitar string, Harley and Punchline fought once again in Eden, a garden Poison Ivy made specifically for Harley in Gotham's sewers. Though Punchline abandoned the fight in an attempt to kill Batman, she still clearly had the upper hand.
5 Booster Gold's Powers & Abilities Give Him The Advantage
A time traveler from the 25th century, Booster Gold fled from his time period in order to become a superhero using highly advanced technology - namely his power suit. Capable of shooting energy blasts, projecting a force field, and possessing superhuman strength and durability, Booster is capable of doing more than just putting on a show.
While it's true that Harley has caught him off guard and nearly killed him (twice), Booster wasn't in the right headspace nor was he really trying. The few times he did stand up for himself, he made it clear that any focused attempt to fight on his part would have resulted in his victory.
4 Barbara Gordon Is Every Bit As Trained As Her Mentor
The first-ever (and arguably most famous) version of Batgirl, Barbara Gordon has the experience and the drive to take over the mantle of the Bat. Having once been paralyzed in one of DC's most controversial stories - The Killing Joke - Barbara kept herself agile, her time spent hacking and monitoring information and the battlefield further giving her even more of an edge in tight situations.
On some level, Barbara completely understands Harley as a person and her situation. Both have been abused and harmed by Joker, and both sometimes struggle with how deeply he's affected them. This also gives Barbara an advantage, however, as she is in a much better mental state than Harley, and can somewhat anticipate her unpredictability.
3 Poison Ivy Is Someone Harley Can Never Be Mad At
Harley's partner-in-crime-turned-lover, Ivy doesn't often go head to head with "Harls" but is sometimes annoyed with her behavior. One of the biggest issues with their relationship is that Harley doesn't always understand the severity of certain situations. Ivy has been known to grow frustrated with the clown princess of crime's relative lack of empathy. Harley and Ivy most recently starred in their own comic book - appropriately titled Harley Quinn & Poison Ivy - and their relationship hit their largest rough patch yet.
Ivy needed Harley to help her during her recovery (as she had just died and been resurrected by Wally West & her connection to The Green) by being there for her. Through a series of hijinks, it was later revealed that Harley had only been helping a "cutting" of Ivy, and was blamed by Ivy for not "knowing her enough." Anytime the two fought each other in the past, Harley has always been unable to bring herself to fight her love, and this time was no exception. It will certainly make things interesting when Ivy returns following the conclusion of Joker War.
2 Amanda Waller Is Called "The Wall" For A Reason
Most famously known as the director of the Suicide Squad, Amanda Waller is a high-level US government agent, often seen in charge of the country's response and protection against meta-humans. Though Waller has no powers herself, she is a master manipulator, strategist, and expert markswoman.
Harley's usually not in any position to fight back against Waller - as most of their interactions occur when Harley is part of the Suicide Squad and with a bomb implanted in her neck - but when she is, Waller outsmarts her by being one step ahead of the game. It's hard to handle or plan any kind of contingency for Harley's unpredictability, something Waller doesn't get enough credit for.
1 Harley's Own Worst Enemy Is Herself
Recovery is a non-linear process, and it's something that has become an essential part of Harley's character. She does what anyone else would do in her position: her best. Granted, there are plenty of ways she needs to keep learning about herself and about how her actions affect others. Her character has certainly come a long way since her debut, but she still has plenty of room to grow.
Though Harley's stability and issues aren't always handled in the best way, it's largely a much more relatable, humane, and realistic depiction of mental illness than some attempts in other mainstream comic series.