Hexwood/Nightmare Fuel

This isn't really a children's book, as such...


 * Reigner One. A kindly, smiling, Eccentric Mentor-appearing old man who... well, see the description under "Complete Monster".
 * The fate of the Servants' mothers: they're impregnated against their will, shot full of fertility drugs to ensure that they have "as many babies as possible," and then never heard from again.
 * Mordion's ENTIRE CHILDHOOD! And yeah, this is in the children's section of many libraries. Sometimes I think of complaining.
 * If Reigner One doesn't get you, and the Bannus itself doesn't leave you seriously doubting your own reality for at least a day or so, Mordion's flashback to the Training From Hell the Servant candidates are put through is absolutely guaranteed to keep you up at nights. His final remaining classmate is "still screaming faintly" after Reigner One is through punishing her for not being able to kill animals in their training, and One's states that he could keep her alive in that condition for at least a year.
 * The fate of Mordion's sister figure. Something about the way it was never DESCRIBED what the Reigner did to her... just that he calmly went to the sink and washed the blood off his hands.