You have to give props to Tatiana Maslany. Not only is she wonderful as Sarah, the main protagonist, but she very convincingly plays the other clones that sometimes you forget that they are all played by the same person. The makeup and effects departments deserve a lot of credit for helping to pull this off convincingly as well, and Maslany herself will be the first to give credit to her double Kathryn Alexandre (who plays opposite her in scenes where there are two clones and is edited out in post-production).
The way "Beth" manages to get herself reinstated to the police force, by delivering a blistering"The Reason You Suck" Speech to the sleazy psychiatrist who prescribed Beth the cocktail of medications that probably contributed to her psychological problems in the first place.
In hindsight Donnie not cracking under Alison's torture and convincing her that he wasn't her monitor. It's as impressive as it is heartbreaking.
The Attack of the Clones in episode 7.
Delphine's sexy spy theme and the fact that Cosima has managed to gather enough information on the clones that her monitor was blindsided.
Helena's cold, steady defiance as she refuses to lure Sarah into a trap.
Mrs. S continues to be awesome.
"Shotgun. Forgot about that."
"That's the lovely thing about this country... Hunting's not just for the rich."
Helena realizing Tomas has been lying to her and that he will kidnap Kira and hurt her if given a chance. She promptly leaps on him and uses all of her assassin training to beating the living hell out of him. It's only thanks to Sarah's intervention that he survives at all.
It's more of a Tearjerker than anything, but Cosima being savvy enough to track down Delphine's true identity, even though it hurt her.
How would you like it if I turned your life inside out?! If I told everyone here that Chad, your husband, slept with the ski instructor long before I did? Well, maybe he acts that way because you BLEW THE ROOFER AT THE CABIN!
Felix's delightful protectiveness of the clones.
Cosima and Delphine collaboratively figuring out the truth behind the Neolutionists' plan, and getting a message to Sarah just in time to stop her signing her life away. Though not in time to save Kira.
It's understated, but after being kicked out of Cosima's apartment Delphine apparently went home, put her sexy underwear spying skills to good use, discovered the ruse, figured out where Cosima was going, and flew across international borders (nobody knows exactly where Sarah lives, so it could have been anywhere from a half-hour flight to the entire continent) to show, rather than tell Cosima exactly what Leekie was up to. She did all this without even bothering to change her clothes at any point. And it's Delphine who first realizes the code is binary.
Sarah avoiding having to make direct contact with Paul by luring him to a bridge, then getting a teen to deliver a phone to him (not without asking for twenty bucks first) and then to avoid DYAD, she gets a teenager to stand with her back to them and when they see she's not Sarah, the teenager has a message to deliver from her;
"She says 'Up Yours'."
Sarah's staunch determination to find Kira. She sneaked into the Dyad event dressed as Cosima, fired her gun near Rachel, pistol-whipped her, demanded to have her daughter back.
Just about everything Mrs. S. does: staging the kidnapping, bringing Kira to a safehouse in the woods, setting up an escape route for them to go to London, killing the Birdwatchers who betrayed her.
When Kira overhears that one of her teeth could help Cosima get better, she doesn't hesitate to tie one off to a doorknob and slam!
Kira: It was already loose.
A small but rather important one: Art says of Tony, "She's a trans clone." Felix corrects him: "He's trans. He's, yeah." This is also a meta one for the writers as the show manages to address a common confusion people have when dealing with transgender individuals without being anvilicious about it.
In 2.09, Helena observes a woman at the Proletheans' compound being abusive to one of the children. Her reaction is a deadpan, "There was a woman in convent like you. You touch her again and I will gut you like a fish". She gets another one later in the episode with her Big Damn Heroes moment saving Mark and Gracie and her Pay Evil unto Evil moment towards Henrik.
Donnie Hendrix confronts Vic and Angela for their sketchy behaviour. "Beth Childs' police business? How about Art Bell? Suspended for doing far less than this. All these women and you just can't put it together, can ya? You don't want to know what we know, and if you come near my home or my family again, I will bury you. Smile. [takes photo of them] Have a shitty day!"
And to celebrate a body burial well done, he bangs Alison on the freezer. Man, Donnie became a huge Badass pretty quick.
A villainous one for Rachel in 2.09: she manipulates Delphine into meeting with Sarah in order to kidnap Kira while impersonating Sarah.She succeeds marvelously.
Ethan Duncan killshimself to prevent Rachel from finding the cipher for his synthetic DNA, telling her in his final moments that she no longer deserves him. And he had her convinced that he had memorized the cipher himself, when actuality he snuck it to Kira who, in turn, gives it to Cosima in the final moments of season 2.