All for Nothing: It turns out that Hector had been working for months to help resurrect Dracula to atone for his betrayal. By the time Isaac comes for him, he has had all of his affairs in order and made it as easy as he could for Isaac to win under the assumption that he would kill him. After everything Isaac has been through since the invasion of Dracula's castle, his Faith in Humanity was Restored and, recognizing that Hector meant well through it all, spares him. While grateful, Hector admits he didn't think what he would do if he survived.
Better to Die than Be Killed: After a well-fought battle, Carmilla stakes herself with her own sword, hoping the explosion brought on by her death would kill Isaac too.
When Isaac admits to Hector that he has been talking to others, he is cutting limes for water, an obvious nod to The Captain he met and befriended in the last season.
The human mercenaries Morana and Striga hired to help in their conquest were some of the forces Isaac killed in his taking of Styria castle. Morana decides to retreat with what soldiers they have left to the lands the mercenaries came from, in order to find refuge and become those territories' defenders as they will be down manpower as well.
Casual Danger Dialogue: After Hector briefly talks to Saint Germain through the mirror, Hector calmly ends the conversation by saying it is time for him to get killed, as he was expecting to die at Isaac's hands.
Chekhov's Gun: Those little stones Hector is seen placing around the castle covertly in his first appearance in the season are used now by Isaac to cut a path right to Carmilla through her castle.
The Coats Are Off: Isaac tosses off his cloak after setting off Hector's escape channel, charging in towards Carmilla.
Cutting the Knot: Or Finger more accurately. Rather than finding some magical means to undo the slave binding on the ring bound to his finger, Hector just cuts the finger off entirely.
A Day in the Limelight: This episode focusses entirely on Isaac and his attack on Carmilla's castle, while the other characters and their storylines take a backseat.
Defeat Equals Explosion: And how! Carmilla's self-destruction creates a shock wave that could be felt from quite a ways away.
Divinely Appearing Demons: Abel, the night creature Isaac uses as a Guardian Entity, just so happens to look very angelic. In the games, it's also known as the "Innocent Devil", based on Abel, the biblical child of Adam and Eve.
Dramatic Irony: Striga and Morana believe that as the castle is sacked and Carmilla is dead, Lenore was likely to have died before Carmilla. They are unaware Lenore is actually alive and well, though a prisoner now of Hector's.
Fingore: Isaac loans Hector his knife so that he could cut off the finger with the cursed ring, freeing him (and by extension his night creatures) from Carmilla's authority.
Flipping the Table: Carmilla throws the big table across the room before killing the monster from Isaac's army.
Forgiveness: Isaac comes to Hector not to kill the man for his betrayal, but to forgive the man for being a victim of other beings machinations and plots. He does ask for help in taking Styria, which Hector provides what he can.
Heal It With Fire: The flames that protrude from Isaac's Forgemaster dagger act as real flames and can cauterize wounds, which saves Hector's life when he cuts off his finger.
Last Villain Stand: Much like Dracula before her, Carmilla stands her ground against her stronghold's invaders and fights to her last breath.
Late to the Tragedy: Striga and Morana come back from their campaign to see Carmilla's explosive death.
Lenore feels protective of Hector as when the castle is under siege, she goes to get him out of there and be safe, rather than helping defend the castle.
After trapping her in a magic cage, Hector repays this by telling Isaac not to hurt her when he confronts him.
Red Eyes, Take Warning: Much like Dracula before her, Carmilla's sclera turn blood red when she fights Isaac.
Screaming Warrior: Carmilla is reduced to screaming madly as she hacks away at Isaac's army.
Screw This, I'm Outta Here: With Carmilla dead, ignorant to how strong the forces that took their castle are, and their doubts as to the chances of her plans for conquest succeeding still lingering, Striga and Morana decide to cut their losses and retire westward of Styria.
See You in Hell: Carmilla says this to Isaac before she dies.
Carmilla: (dripping with ice-cold fury) You don't deserve my blood. And when you do die and go to Hell, I'll be there waiting for you. With a sharp bloody stick, and a determination to find out if you can die twice.
So What Do We Do Now?: Morana asks this after Carmilla's death. They opt to not even send scouts to the castle and leave the presumed dead Carmilla and Lenore.
Carmilla could have easily taken Isaac on her own, but battling a constant stream of his monsters gradually wears her down.
Hector fully expected Isaac to kill him for his role in Dracula's death. He's thus completely confused when Isaac not only spares him, but forgives him for it, since he was manipulated by Carmilla. While he's clearly grateful, he genuinely has no idea what to do with himself afterward.
