While every character in The Witcher has a certain level of badassey to them, no sorceress manages to convey this more than Anya Chalotra's Yennefer. Brought up by an abusive family and led to believe she was worthless due to her elf blood and her "twisted spine", she had some severe problems. She was recruited as a sorceress and managed to leave her past behind, growing into one of the most powerful mages the continent has ever seen, and she demonstrates how awesome she is time and time again over the course of the first season.
Of all the moments Yennefer is a badass, these are the scenes that truly show it off.
Her Transformation
Yennefer chooses to undergo painful enchantments to change her appearance into something more conventionally beautiful, knowing it will make it easier to climb the ranks of a royal court and to enchant people into trusting her. While most sorceresses would typically be knocked unconscious for such a transformation, Yennefer elects to stay awake for the quickness of the procedure, and she endures her bones twisting and cracking to form her into something new.
It's a clearly agonising procedure and although she screams all the way through, she somehow emerges alive.
Attempting To Save The Baby
When the king she serves decides that he's sick of his queen only giving him daughters, he sends an assassin to kill both the queen and the baby. Yennefer attempts to save both initially by opening up portals and dashing through, but the assassin follows. When the queen screams at her, ungrateful and selfish, she leaves and returns only to try and save the baby.
She sadly fails, but her efforts show off her amazing magic.
Rejecting Istredd
Her romance with Istredd is prominent throughout the first few episodes and, to his credit, he doesn't love her for an enchanted appearance but truly for who she is. When he reveals her elfen blood and she loses her position at court, he suggests traveling with him and rather than grasp onto anything she can, Yennefer rejects him with some cold words, describing a life with him as, "a slow suicide."
It's harsh, but did he truly expect Yennefer to be happy following him around while he did his own research?
The Djinn
Yennefer is never happy, never settles. She claws her way to power and wants more and more of it constantly and when she comes across a Djinn, she tries to absorb her. The Djinn is slowly killing her when Geralt arrives to try and save her, but she refuses to give up and when asked what it is she wants, Yennefer screams, "I want everything."
For a woman who's never had anything and now seems to have everything potentially within her grasp, we can't help but admire her.
Fighting To Protect The Dragon
To undergo the enchantments that altered her appearance, Yennefer had to give up her ability to have children. She hears rumors that a dragon may provide the cure to this and goes in search of killing one, but when she finds the dragon already dead and its mate ready to protect the egg left behind, she fights for the dragons instead. She and Geralt have a scene where they fight off the enemy together and we see that not only is Yennefer a talented mage, she's pretty handy with a blade too and not afraid to use them.
Leaving Geralt
She's not weak for Geralt either, even though she's in love with him.
When finding out that he used the Djinn's last wish on their relationship, she questions her sense of free will in terms of loving him and makes the choice to leave him. It's not a visually stunning scene with flames and blades or anything of the sort, but truly a testament to how awesome she is that her free will means more to her than anyone and she turns and storms off.
Will it last? We doubt it — Geralt and Yennefer will see each other again. But it was pretty awesome in the moment.
Turning Tissaia Down
Although Tissaia is a pretty awesome character, she was abusive to Yennefer at the start, if only to make her a good mage. Therefore, when she comes to Yennefer seeking her help and telling Yennefer it's her chance at redemption, it's pretty satisfying to see Yennefer finally able to stand up to her and refuse her.
Return To Aretuza
Her return to Aretuza is brief when Yennefer is requested to go there by another mage, but she makes an impression even so. She connects with some of the students there and although she's brutally harsh (but honest), she seems to take some of the control back by calling out everything that's wrong with the place and revealing some of its secrets.
Satisfying, for someone who was once so deeply under its awful control.
Any Time She Opens A Portal
Yennefer can open portals to travel, and seems to find it easy due to her blood. Sometimes its accidental but as she learns more and more about the ability, it becomes controlled, and it's one of the most awesome powers we see a mage have. It's also visually impressive to watch her open the portals and run through in times of need.
The Battle of Sodden Hill
The series ends on the Battle of Sodden Hill, where the mages make a choice to stand against Nilfgaard. It seems as if they'll lose when Nilfgaard begin to gain the advantage, until Tissaia tells Yennefer she can save them. Yennefer has always been taught to bury her emotions, to bottle up her chaos, but on Tissaia's advice, she lets it fly free. Flames come from her and engulf the enemy entirely while Yennefer cries and screams, and she immediately disappears, leaving the corpses of Nilfgaard soldiers unable to continue on with their conquering for the time being.