The Hero of Oakvale destroying Jack's body while Jack was wielding the Sword of Aeons. William Black pulled off the same feat long before then, but he had to steal the Sword and then wield it against Jack to do it. In the canon ending, the Hero even destroyed the Sword afterwards. The Hero of Oakvale later fought Jack in his Dragon Form and defeated him, followed by tossing Jacks mask into the lava, completing Jack's destruction.
Hammer avenging her father's death simply by killing Lucien's envoy with a swing of her mighty hammer.
The fact that your hero was shot out of a castle window, fell some odd feet to the ground, and survived.
The Hero of Brightwall gets some truly badass Finishing Moves. Shall we list them all?
When fighting against a Balverine, one of the finishing moves is to do some sort of freaky back-flip-face-kick, then pin the Balverine's chest between your feet, roll over mid-air, and faceplant them into the ground, breaking their neck. That is the definition of the word awesome.
How about when you're fighting a human enemy? One of the finishing moves is to jump up on his/her/its shoulders and snap his/her/its neck with your knees.
When fighting a Sand Fury, one of the counter-finishes has the hero waiting for them to do a cartwheel over the hero, then reaching up, grabbing the fury's head, and snapping her neck in mid-cartwheel.
Successfully managing to make all the good choices and still make enough money to save everybody at the end of Fable III.
Personally, this troper finds that beating the main quest without getting knocked out at all counts.
If the player can pull it off without breaking any promises, this is the definition of a CMoA for any ruler who is facing the apocalypse and who has been left with the Weight of the World on her/his shoulders.