Dakota North is introduced this way. She's a Badass Normal private detective who more than holds her own against thugs and assassins, especially in her debut series.
Elektra is an Olympic-level athlete and gymnast, proficient in many martial arts and master of many different weapons.
Fantastic Four: Susan Storm sure started out as a Faux Action Girl, but man did she ever level up. She's now the toughest fighter on the team, and she's on a team with Ben Grimm.
It's a bit more complicated than that. She's the most powerful person on the team, but that doesn't necessarily mean she's the most ruthless or skilled fighter. If she's aware of a threat and willing to cut loose, she can kill with a thought, but she'd much rather create barriers to protect her friends or restrain her enemies.
When she fought Wolverinein his own book, he turned tail and ran because she had his number. Sue wins.
Captain Marvel: Carol Danvers is an interesting case. She was originally introduced as the "Veronica" love interest for the original Captain Marvel, and an ex-Air Force major and security officer with NASA: as such an objectively strong character, but one who frequently got Overshadowed by Awesome when Marvel duked it out with the supervillains of the week. So Carol came to wish that she could be her lover's equal—And got the wish, as a piece of malfunctioning leftover alien machinery transformed her into a Kree Super-Soldier of the same type. Now she is a standard Flying Brick character, but the stories in which she shows real strength tend to be flashbacks to her days as a pilot: merely human, but making it count.
Mockingbird: Bobbi Morse may originally not seem like much, but you have to remember, she spent most of her life without powers of any kind.
Nextwave: Elsa Bloodstone to stupidly ridiculous proportions, kicking the ass of anything with an ass using anything from shotguns to shovels to guitars.
She-Hulk: Any of the She-Hulk's, whether it's Jen, Lyra or Betty Ross.
Originally, She-Hulk/Jen was really just a brawler but due to her time on various superhero teams she has picked up a lot of fighting skills — such that she effortlessly disabled a mugger, while still in regular human form.
Spider-Man: Black Cat. Even though she doesn't have superpowers that can be directly used in combat. She also counts as a Dark Action Girl, depending on where she is on the morality scale.
The Unbeatable Squirrel Girl: Squirrel Girl is a superb hand-to-hand combatant capable of taking down Deadpool and Wolverine in a one-to-one no-claws fight.
Ultimate Fantastic Four: Right off the bat, Susan Storm is much more assertive, is a biologist at the Baxter Building and almost immediately realizes her full potential as the most powerful member of the team.
Blink's powers make her extremely effective in fighting the Sentinels, both in taking them out herself and assisting the others in fighting them.
Mystique is the only mutant back in the past who's been doing anything for the last few years (Magneto has been incarcerated inside the Pentagon for a decade, and Xavier's been moping around the house since the start of The Vietnam War). Even when the plot takes off, she's still the most active character.
Mystique knocks out a few guys who are bigger than her in East Berlin. She later becomes the battle commander of the X-Men.
Jean Grey unleashes the full power of the Phoenix and obliterates Apocalypse, who can only marvel at her power.
An unarmed Agent Moira MacTaggert, who is covered in a niqab that hinders her movements somewhat, is able to disarm a man larger than she is and render him unconscious.
She might be the smallest Action Girl in the whole film series, but X-23 from Logan is very much a Little Miss Badass proving to be just as savage as her clone papa Wolverine. She even kills Logan’s Evil Counterpart X-24 at the end.
Tony assembles the Mark 42 around Pepper in one scene, which she then uses to save Tony. Pepper also gets injected with Extremis later, allowing her to save Tony from the similarly super-powered Killian.
From the Guardians of the Galaxy films, Gamora and Nebula, adopted daughters of Thanos who were raised and trained as assassins.
From Doctor Strange (2016): The Ancient One, as well as Tina Minoru and the female Zealots.
Black Panther gives us Okoye, the commander of the Dora Milaje, and Nakia, an exceptional Wakandan spy. Even T'Challa's little sister Shuri, whose primary aptitude is in designing Wakanda's incredible technology, proves herself capable of combat in the film's climactic battle.
None of the aforementioned women can hold a candle to Carol Danvers, the eponymous Captain Marvel. She is touted as the most powerful character in the entire MCU, even more powerful than Thanos.
Live-Action TV
Agent Carter: Peggy Carter herself. She's more than competent with her fists, a revolver, or anything else that's handy at the moment. Part of the reason Peggy is so good at winning fights is because the series takes place in post-World War II America, where sexism was rampant and women were expected to Stay in the Kitchen. Peggy is particularly dangerous because nobody expects her to be.
Melinda May, SO HARD. Skye slowly becomes one, too, but May is on a whole different level, being pretty much the most formidable hand-to-hand combatant in the series. If you're not superhuman, she will DESTROY you.
Season two introduces Bobbi Morse, who's just as badass as ever. Her first scene has her taking down a bunch of HYDRA soldiers with ease.
Once Skye fully takes up her identity as Daisy Johnson she quite firmly is put on May's level, arguably even higher due to her superpowers.
Legion has Kerry Loudermilk. On a series where most of the mutants have some kind of psionic power, she's just really strong and a preternaturally good fighter, enough to take out a whole unit of soldiers at once.
Wanda herself, in fact she takes a level in badass in the finale when she fully embraces her Chaos Magic and becomes the legendary Scarlet Witch whose power quote “exceeds that of the Sorcerer Supreme”.
When captured by SWORD Mooks, Monica Rambeau knocks them out quickly alongside Agent Woo. After reentering the Hex, Monica gains her superpowers from the comics being able to manipulate energy to the extent where enemy bullets pass painlessly through her body and to the ground.
Darcy deserves a mention as she puts her Car Fu skills to good use smashing into General Ripper Hayward with a food truck as he tries to escape justice in a humvee.
