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Tear Jerker: Magic Kingdom of Landover
The final chapter of The Black Unicorn, particularly the last line: 'Some of them passed it on.'
The Tangle Box, after Ben, Strabo, and Nightshade recover their memories of who they are. The witch's genuine pain, rage, and suffering were absolutely heart-breaking to read.
Witches' Brew, when Abernathy realized the only way he and Questor would get back home was if he allowed the wizard to turn him back into a dog again. The very simple, direct, resigned way he 'closed his eyes, felt the change, and let the magic take him' was so brave, and also so very sad.