In "One Way", she uses her resolve and polyglot-skills to get Michael arrested, thus saving his life by stopping him killing Kasim Tariq.
She breaks out of her chains and bursts out of Division, but not before taking out the whole training room full of recruits and guards in "All the Way".
In "Coup de Grace", she takes out two members of a Division assassination squad toting submachine guns with a sword. Bad. Ass.
In "Pandora" Nikita walks through the CIA's front door, convinces the receptionist to let her talk to someone, defeats a sleeper agent, stops the Director of the CIA, Ryan Fletcher and two other bigwigs from being killed by the nerve gas, and escapes the CIA.
She dislocated her own shoulder to escape Michael in "Kill Jill."
Though it slips into the creepy and scary territory a bit, Nikita's response to being tortured by Brant in "Wrath" is downright amazing. After she fails to talk him down rationally, her inner badass takes over and she rips him apart so badly that he is seen holding back tears by the end of her speech. The scene can be enjoyed here in all its terrifying glory. The crowning moment starts with the following opening quote.
Nikita: (mumbles) S-Sorry... Brant: (comes close) What did you say? Nikita: (lifts her head slowly) I'm sorry...I'm sorry I didn't take out your other eye.
When Nikita rescues Birkhoff from the FBI in 2x20, the following happens:
Birkhoff: What are you doing? Nikita: I'm gonna save your ass so I can kick it later!
Infiltrating Division in "Crossbow" to shut down Percy's Kill Sat, which culminates in blowing the server room to hell. It's even more impressive than it sounds.
Remember that opening monologue we heard dozens of times about "the last word they breathe before the end will be my name"? Guess what both Percy and Amanda say before we see him plunge to his death and she gets locked away forever, respectively.
In the series finale, after Nikita explains to Ammanda how she won, she ends with one last dig before leaving her in a supermax cell, in a cruel Call Back to Ammanda's origin.
Nikita: Welcome back to the basement...Helen.
In "Clawback", Michael takes out several members of a Division strike team from a rooftop one building over, after being drugged by Nikita.
"Covenants": Single-handedly taking down all of Kasim's guards, saving Nikita in the process.
His Big Damn Heroes moment in "Guardians". He comes out of nowhere, kills 3 GOGOL agents in seconds while driving a car, and saves Nikita and Owen.
How he anticipates Percy, Carla and Division's actions during a prisoner swap; he had to work for it, but he threw a major spanner into the works and got the hostage out safely.
One of Michael's recruits came for a fight in 2x21 and made the mistake of referring to Nikita as "that ass." Michael then promptly broke the punk's neck.
In "Homecoming," he earns yet another moment by locking down the command center of Division armed with a grenade and an unshakable sense of logic.
While handcuffed, he charges a bunch of cops to recover Nikita's engagement ring.
Percy gets props for not flinching when she opens fire at him. Even though he knew the glass was bullet proof that was some serious nerves of steel.
In "The Next Seduction", he reveals the plot was a Batman Gambit he set up in order to get Nikita to do his dirty work for him. True, she then beats him anyway by playing Division and Gogol against each other, but he still gets credit for managing to Out Gambit her in the first place.
In "Pandora", he shows he's not all talk, as he's able to go hand-to-hand with Michael for several minutes before being knocked out.
In "Looking Glass", he manages to make putting on a suit look badass, while a Theme Music Power-Up plays. "It's a start," indeed.
His plan in "343 Walnut Lane", manipulating Amanda, Alex, and Nikita simultaneously, and resulting in getting Alex under his thumb.
His whole scheme in "Sanctuary" is quite impressive, but his true crowning moment in that episode is his "The Reason You Suck" Speech to Amanda. He nearly drive her to tears.
"Doublecross": He's captured by Team Nikita and tied to a chair, just waking up from being chloroformed. Birkhoff takes a swing at him... and he quickly moves his head so Birkhoff's fist hits his forehead rather than his more vulnerable face, causing more pain for Birkhoff than him.
Waltzing into Division and taking it over again with some choice tidbits about Amanda's daliances with Ari. If there was ever a scene where you were completely rooting for him, it's this one.
His plan with the Crossbow Kill Sat, which effectively makes the President his bitch. Plans within plans within plans.
In "Resistance", Alex breaks out after being captured and tortured by "terrorists" in a training exercise. She then sustains running 9-minute miles for close to an hour- in the middle of the woods, barefoot, at night. Yes, running away can be badass.
And in the following episode, during her Journey to the Center of the Mind, she has a confrontation with a dream version of Jaden and kills her. Considering Jaden's The Scrappy, lots of fans were cheering at that, while at the same time, wishing it had been for real.
In "Into The Dark", she manages to beat a supposedly unbeatable lie-detector. And she does it by technically telling the truth.
She gets a small one in "Betrayals" before the wham and HSQ kick in: Amanda has her strapped to a chair and has just electrocuted her. In walks Percy, wanting to know what's going on - and before Amanda can open her mouth, Alex calmly explains who she is and how Amanda figured it out, thus stealing her thunder. This causes Amanda to lose her cool for once and slap her.
All of Origins. She evades an assaination attempt, pulls a Click Hello on Ari, and then shoots her way out with minimal backup from Division and Micheal.
"Homecoming": Alex guns down multiple Division agents, kills one with a pitchfork, and fights Roan hand to hand. Even when he breaks her arm she still keeps fighting. She kills Roan, who Nikita is scared of.
In "Self-Destruct", still reeling over Sean's death and Amanda's programming, Alex carves a bloody path through a gang of drug dealers and human traffickers, culminating in an impressively ninja raid on their base of operations. Even better, she begins with her patented "helpless female" opening before calmly kicking ass.
In "Glass Houses", she lets Alex think she'll get away with killing Jaden and when she starts to leave she reveals she knows who Alex really is and that she's working with Nikita. Next moment Alex tries to fight her and escape and Amanda easily knocks her to the ground with just one blow.
In "Pandora", she reveals that her true loyalty is to herself when she stops Alex's heart with the electroshock chair, and then restarts it with an adrenaline needle, tricking her tracker/kill chip into not working anymore.
In "Pandora" he frees Michael and decrypts the Black Box for him; not a coward indeed.
Followed up by hacking the CIA in order to help Nikita escape from their headquarters.
Saving Nikita and Michael with a pair of remote controlled spy planes, followed by personally insulting Amanda after spending the episode insisting Division be told he's not working with Nikita.
Fighting off a trained Division agent with his bare hands and some computer parts. He loses, true, but he lasts longer than you'd expect.
While being tortured by Amanda in "Fair Trade" he does beg for his life, but he doesn't give up Nikita or the black box.
In Origins, Birkhoff tells Carla: "Give my hardware back. Now. Bitch." while holding her at gunpoint.
In the next episode, he then shoots her when it's clear she won't stop betraying Nikita to Percy.
In "Shadow Walker" (S2E20), he kills a Division agent with his bare hands and judicious use of a stairwell, then shoots another to save Nikita. This after he froze up and got her shot earlier in the episode. Looks like all that sparing with Micheal finally paid off...
In "Homecoming", Sonya asks him to help her with something and he marches right up to her, grabs her, and kisses the living daylights out of her. Go Birkhoff.
In "Broken Home", some of the mutineers decide to kill him rather than risk him reactivating Shadownet. Birkoff calmly disarms the agent closest to him and calmly asks if the man knows what it's like to kill someone. The agent says "no", and Birkoff shoots the other agent, knocks out the one he was talking to, and escapes.
In "Clawback", he shows he is indeed a genius analyst by figuring out how Oversight makes its money. By itself, not that impressive, but he does it from behind bars, with nothing else to go on than access to the TV news and some newspaper cutouts.
His Dying Moment of Awesome in the penultimate episode, breaking his thumb to escape a restraint, getting the better of Amanda physically, fighting through all her henchmen, and when he's finally captured he beats up the henchmen again and suicidally jumps out a window so he can tell Nikita what's going on with his dying breath.
Roan gets two in the pilot episode: The second and more blatant one is his casual slaughter of three armed bodyguards of an African diplomat. But the first and more subtle one is Nikita's reaction when she sees him.
Holding his own against Owen Elliot in "The Guardian" is another: though Roan loses the fight, the fact that he went toe-to-toe with an extremely pissed off Guardian speaks volumes about his skills.
Bonus points for surviving that fall and walking away unscathed.
When Nikita spies on a clandestine meeting between Percy and a client Senator in "Phoenix", Roan notices an active speaker phone, determines that she's in the vicinity, and is quickly in pursuit.
Roan in "Partners": putting Nikita on the retreat and detecting Gogol agents that Alex doesn't notice, killing one without even looking.
In "Clean Sweep", he brazenly admits his loyalty to Percy, kills Division operatives, and sends Alex fleeing in fear.
Another subtle one in "Shadow Walker": Percy's accountant nearly faints when Roan exits the car to confront him, cementing his reputation as The Dreaded.
"Homecoming" depicts Roan's biggest moment of awesome: When he attempts to initiate a nuclear meltdown on Percy's orders, he is attacked by Alex and Sean. Despite their respective skills as Nikita's protege and an ex-Navy SEAL, they are quickly and methodically dismantled by Roan in close quarters combat before he dies, leaving both of them in an exhausted, wounded heap on the floor.
Ever since we've seen Sonya, she's been strictly tech-based, and is damn good at it, but never have we seen her in any actual combat situation or even training. Then comes the episode "Broken Home", where the mutiny in Division reaches a boiling point and violence breaks out. Agent-turned-rogue Chris starts beating Birkhoff and attempts to kill him, and Sonya reacts by grabbing a nearby MP5K, fills Chris with bullets and looks stunningly kickass while at it.