It was a huge Moral Event Horizon for the Targaryens (so much that Aegon wished he hadn't green-lit it), but the executions of the Westerling Family and Roslin Frey, as villainous as it was, single-handedly managed to win over nearly all of Westeros to Aegon's side, and destroyed the near-invincible Lannister/Tyrell alliance. And all it took was for one girl to make an escape for her life.
Jaime Lannister, while trying to stop the executions from being carried out, angrily charges in and kills off three of the Kingsguard men. Despite losing his sword hand and the grievous wound inflicted on him by the Brotherhood, he still rushes in, knowing the consequences of treason, and kills all three at once!
And then there's the Freys' reaction to the executions. Walder Frey just ups and dies an immediate Karmic Death after hearing of Roslin's murder and Jeyne Westerling's escape from Riverrun, effectively nullifying everything they've earned from the Red Wedding. Edwyn Frey, newly made Lord of the Crossing, leads two dozen of his own relatives frothing for vengeance over the Lannisters' betrayal...and are soon hanged by the Brotherhood Without Banners. There truly is no better way of serving karmic justice to the House that redefined treachery in Westeros.
He gets another one in the same chapter where he not only holds off against Mance Rayder with the real Lightbringer and kills him, taking his sword with him, he fends off a surprise attack from a really pissed-off Nymeria and wounds her with his newly obtained weapon.
Tormund Giantsbane calling out Bowen Marsh for his cowardly act of killing Jon Snow, after all that he had done to try to establish an alliance between the Night's Watch and the Free Men. He then makes it clear to Marsh and the 'crows' that they will never, ever force them back beyond the wall without any bloodshed.
Sansa Stark finally beating Littlefinger at his own game when the Burned Men and Brotherhood assault the Eyrie. Which ends with him meeting face to face with a very angry Lady Stoneheart
The North Remembers is one long CMOA for Sansa Stark period, from the moment she grabbed a hold of Ser Shadrich's knife while he was trying to rape her, and killed him in the process.
In Chapter 67 Theon, having survived Ramsay's explosion of Winterfell, finds himself cornered by wights. Believing this to be the end, Theon prepares to go down fighting, and proudly states his name at the wights...That is when Stannis arrives and proceeds to cleave his way through every one of the wights
"The fiery heart on his breastplate took the brilliant luster from his sword, and for that instant, he was in truth a warrior of light. No one had ever questioned Stannis, or any of the Baratheons, for their skill in battle. Ours is the Fury."
Chapter 76, Sandor single-handedly charges the Targaryen forces landing on Blackwater Rush, and manages to wound Aegon in the process. Not only does Sandor survive, but this causes the Targaryen army, which was on the verge of taking King's Landing, to retreat
Chapter 89: As the Others begin pouring through the ruins of the Wall, Melisandre sacrifices herself by turning into a pillar of fire in order to give the remnants of the Watch a fighting chance as Sam rallies them for a final stand.
Sam: To arms, men and women of the Watch. To arms.
Chapter 94 The wights are assaulting White Harbor, and Wylis Manderly ends up dying in Jeyne's arms, all seems lost...Cue Nymeria and her wolf pack arriving to save Jeyne and help drive the wights out of the city.
Chapter 95 Theon finally killing Ramsay. Twice. The second death occurs after Ramsay had turned himself into an Other-like lich by drinking Davos' poisoned blood. Theon and Asha try to escape but are cornered by Other!Ramsay. It is in that moment that Theon rekindles Lightbringer using his and Asha's blood and uses it to finally end the Bastard of Bolton once and for all.
Chapter 97 As he is about to be sacrificed to awaken the stone dragons at Dragonstone, Jon Connington reveals to Aegon that he is not a Targaryen but in fact descended from the Blackfyre line by way of Illyrio and his Lysene wife, and that Varys, himself a Blackfyre had been playing him this whole time. Aegon decides he's had enough of Varys' counsel and calls off the sacrifice, only for Varys to call on Elia Sand as a substitute. With no other recourse, Connington willingly sets himself on fire and tackles Varys, killing himself and Varys and giving Aegon two dragons to control.
Chapter 101, though it's also horrifyingly sad, Jaime Lannister, despite being badly injured, musters enough strength to once again save King's Landing from an insane monarch who wants to burn it to ashes with wildfire.
Chapter 102 Arya refusing to kill the Summer Maid.
Arya’s hand trembled. One more. The easy thing to do. End the threat that had stalked her from Braavos. One more. She had killed and killed until she couldn’t tell apart the faces, until they had only become a blur. One more. Kill the woman who had become her. Who was her. One more. As if it was so simple. As if she wanted to. If this wasn’t merely another lie. One more. Look where it had led her. What it had made her.
She would rather forget everything, and learn it anew, than to remember it like this.
She opened her fingers. Let the dagger clatter to the deck. And with one whispered word, defied the Faceless Men one last time.