Magrat injects a little life into a thick wooden door, promptly blowing it off its hinges. Thus begins a once-per-novel tradition of Magrat showing why she's a witch by doing something crazy awesome.
Death's candid admission towards the end.
Insane Duke: If I'm not a ghost, what are you still doing here? Death: Waiting.
Surprisingly, the Duke manages to pull one while in the face of Granny Weatherwax. She had suspected that he was a weakling beneath a guise of strength, but was completely unprepared for him being so insane that it had refined what little sanity he had left into, "ice in the heart of a blazing furnace," sanity so cold and hardened that it came full circle and became a terrifying and powerful form of madness.
He manages to out-stare Granny Weatherwax. Something only a living country manages to also do within the book.
Nanny Ogg knocking Lady Felmet out with a cauldron, in the middle of her Evil Gloating.
"She does go on, doesn't she?"
The Fool stepping up to be King has to count as one. This man was so put-upon by everyone from his family to the Guild to the Duke and Duchess that he walked stooped over and wasn't even brave enough to talk to Magrat at the beginning of the book, but at the end Lancre needs a king and he's Tomjon's brother and even if the only thing he knows about being a King is that it has to be better than being a Fool, he's going to try to do it right. Then he goes to see Magrat and tells a sergeant he'd inherited from the Duke (who was something of a Psycho for Hire, or at least Pyro For Hire) to stop telling him to burn things, to stop interfering in his business, and to go to Ankh-Morpork on a "special mission."
The three witches moving the entire kingdom sixteen years forward in time. The prose really gives a haunting sense of the power and strength they possess.