YMMV / The Doomspell Trilogy

• Complete Monster: Dragwena is the wicked ruler of Ithrea, and one of the vilest Witches of all time. Banished to a black-and-white world she called Ithrea due to her propensity to raise up fanatical armies of Child Soldiers in the war of the Witches and Wizards, Dragwena promptly turned to stealing thousands of magically latent children from Earth to trap them on Ithrea. Dragwena enslaves and torments the children in every way imaginable: distorting their ages; forcing most of them into the horrible wilds of Ithrea to gather food for her; and wasting the lives of entire generations of children in grueling slavery to build her massive temple. Dragwena has slaughtered countless thousands of children through sadistic trials and torture in preparation to steal the magical "child-hope"—a young girl named Rachel—that will allow her to conquer Earth. Dragwena attempts to utterly massacre a group of rebellious children who call themselves the Sarren as well as everyone tangentially connected to them; tries to corrupt Rachel into a Witch who will enjoy killing children as much as she; and even when Rachel finally beats her, Dragwena homes in on her eight-year-old brother to snap his neck, vowing she won't die without killing one last child.
• Nightmare Fuel:
  • Dragwena in general, and what she does to all of the children in The Doomspell.
  • The Griddas in The Wizard's Promise are essentially bigger, toothier, heavily-armoured versions of Witches. The first two books made the Witches absolutely terrifying, so... yep.
  • In The Wizard's Promise Eric discovers his power to literally unmake magical beings.
• What Do You Mean, It's for Kids?: There's a fair bit of death, often described in gruesome detail.