Like some others of the 'honed physical ability' class of heroine, Nightgirl tends to rely on superior hand to hand fighting ability, acrobatic ability and the use of gadgets and devices to subdue villains, rather than any inborn superhuman powers. 

Willow herself has studied a variety of martial arts and fighting styles, from Aikido to Kung-Fu, and she is constantly honing new moves and learning new ways to use them.  She has gained exceptional acrobatic skills through similar training, getting her body to the point that thought and action are one almost as second nature. 

In her belt pouches, Nightgirl regularly carries the essentials for her profession-- including blunt and bladed shurikens, CO2-operated grapnel gun, smoke pellets, tracking devices, and other supplies that she finds use for when solving crimes, such as an infrared pocket light, disposable second-skin gasmask, lockpicks, eavesdropping equipment, and GPS locator.  Her cowl comes equipped with nightvision overlays and an embedded communicator with transciever and police bands, as well.
 

Willow Hannigan was constantly plagued by nightmares throughout her youth.  Without fail, when the nightmare began, she would see a terrifying vision of a creature with long pointy ears and a flowing, formless black body.  He was always fighting crowds of men, and then, when done with them, would turn to her and slowly glide over and loom over her, as she remained helpless, unable to move.  One evening after she got home from school, Willow turned on the news to hear reports of such a thing being spotted in her home town of Gothic City.  The nightmares seemed to all flow back to her, and she was terrified.  For weeks after the first report, she refused to go out at night. 

But terror couldn't keep her hostage forever, especially when real life has to be lived.  One autumn evening while at a Student Council meeting, she lost track of time discussing a project with a teacher, and missed her ride home.  Repeated attempts to call for another proved fruitless, and she was forced to make the ten-mile walk through town to her neighborhood.  While her nightmares might have been at the forefront of her mind, less dream-like problems soon cropped up.  A group of street toughs, seeing a young woman walking the streets by herself, decided to make a play for her purse... among other things.  Willow was attacked by the gang-members, pushed into a back alley, knocked to the ground, and while they went through her purse and leered at her, she found herself too frightened-- both of them and the thought of what they might have in mind for her-- to get up and try to escape.

When they found out that she didn't have anything of value except herself, it became plainly apparent that would more than be adequate for them.  The assailants were almost upon her when, suddenly, the creature from her dreams appeared, casting a fierce shadow from the streetlights as it descended.  Using the momentary startlement of the punks to its advantage, it made short work of all of them, leaving them unconscious in the alley.  The black creature loomed over her.  Willow half expected to be killed, and half expect to just “wake-up” as she always did at this moment.  Instead, the seemingly formless creature extended his hand, and lifted the girl to her feet.  She simply stared at him for a while, and in the next moment, the creature was gone.

Tales of the creature, nicknamed Night Terror by the media, began to grow, and Willow-- who found herself morbidly curious despite her earlier fear of him-- saw the pattern: every time the creature attacked, it was to defend an innocent, or stop a crime.  The creature she had feared for so long was not the evil thing, she realized!  Inspired by Night Terror’s actions, and also convinced by the near-assault on her, she devoted herself to no longer be helpless, and also to help others.  She trained rigorously, and found herself to be a much more apt student than she could have hoped.  And buoyed by her training, she fashioned her own costume in the form of Night Terror as best she could, and set out to help.

Her fighting skills were good, and her acrobatic abilities were exceptional.  Even though her first few outings were somewhat mistake-prone, she treated them as learning experiences and resolved not to make those same mistakes twice.  And over time, she began to succeed at that.  She even used the public's hysteria over the appearances of Night Terror to her advantage, finding that she could cause criminals to get weak-kneed if they saw a shadow falling toward them like a creature of blackness, thinking that Night Terror was after them and might drain their blood or something.  All the while, during the days, Willow studied more about criminal techniques and police procedures, the better to apprehend those who fought on the wrong side of the law.

And while she fought for justice at night, unbeknown to her, another was watching over her.  One day, after tracking a sadistic murderer who called himself the Jester to a darkened warehouse, Willow dropped in, only to find that the Jester turned the tables on her and was waiting for her to come out into the open.  Switching on the overhead lights of the warehouse, the Jester pointed a gun at her and told her with a cackling laugh that he'd realized she was the one following him.  And now the joke was on her.  And with that, he fired.

And suddenly, everything went black.  For a moment, Willow thought that she'd died, and the air whistling around her was in fact, her spirit rising from her body.  And then she realized that death had extraordinarily tightly-muscled arms.  She then realized, as she pulled her head back from the darkness of the cape of her savior that Night Terror had swooped down from above to save her at the last moment.  He dropped her off near the warehouse dock doors, apparently expecting her to make her escape, and rushed back to where the Jester had been seen. 

But Willow wasn't about to let him go that easily this time.  Although he was fast, she followed behind, wordlessly, and arrived in time to see the cackling Jester spray Night Terror with some gas from a trick flower in his lapel.  As Night Terror stumbled, blindly, the Jester again raised a gun and laughed.  And at that moment, seeing her twice-over dark savior needing help, Willow didn't think.  She acted, rushing forward and launching a roundhouse kick that sent the Jester's gun clattering away into the darkness.  As he laughed at her, she sent an uppercut into his jaw that caused him to bite his tongue, and followed that with an elbow into his chest and a follow up hand strike that left him teetering, then falling to the ground, unconscious.  She then helped Night Terror back to his feet.

He looked at her.  Nothing else.  And even so, it was still terrifying... for the first time, Willow could understand why criminals wet their pants at the mere sight of him.  But even though Night Terror again loomed over her, she stood fast.  And then, with another gesture, he again extended his hand. Thus the silent pact was formed, and Night Terror had his new partner: Nightgirl!

Nightgirl continued to study detective work and crimefighting, but now, she was under more expert tutelage.  And it showed, as soon she began to make a name for herself in her own right.  That notoriety apparently had its perks, as Nightgirl was eventually visited by a pair of fellow teen heroines from nearby Hub City, Adventure Girl and Bubbly Blonde.  Meeting the dark heroine on a roof of a gothic church, the Teen Twosome invited her to join their “club” of other teen girls looking to help each other in their task.  At first, Nightgirl wasn't sure about it.  But after some soul-searching and discussing it with her mentor, she called the two back and accepted their offer.  While Nightgirl’s first allegiance is to Gothic City and her partnership with Night Terror, she also plays an integral part in Team: Teen as a strategist and stealth specialist, as well as a valued hand to hand combatant. 

Nightgirl, following the lead of her mentor, has two seemingly distinct personalities.  Willow Hannigan, the person she is without the mask, is a responsible, but fun-loving, teen that does everything one would expect of a high school girl.  She enjoys music, talks on the phone, likes to be on the run, and hates homework and schoolwork... even though she excels at both.  Nightgirl, on the other hand, is all business.  While she still has moments of levity-- especially compared to Night Terror-- she is a quietly competent and driven young woman who takes her costumed life seriously and has very little lenience for criminals.  As she continues to hang out and become more comfortable with her teammates in Team Teen, a bit more of her Willow personality has come into the open around them than she usually displays.  But when crime strikes, it immediately gets shelved in favor of the justice-seeking Nightgirl side. 

Nightgirl also feels a strange bond to Arachnid and Psykique, a pair of heroes she's met since becoming Night Terror's teen sidekick.  She’s not sure why that is, as she hadn’t met them until very recently....