Every Diana Wynne Jones novel has a villain. Jones herself was of the opinion that there are truly toxic people in the world, and kids need to learn how to deal with them. So the villains of her stories are utterly, squirmingly real. You know them, or you’ve heard about them from someone, and you recognize the truth of their existence on some deep level.
I think that the central feature of a Jones villain is that they believe the world should be a certain way, and they will not countenance a world any different. If everyone should be well-behaved, they will make everyone well-behaved. If this or that should belong to them, they will take this or that and be baffled and hostile to any suggestion that it isn’t their due.
Somehow, Jones is practically always able to balance a fascinating cognitive dissonance in her villains. None of them consciously acknowledge that the world is, in fact, not exactly as they imagine it. Thus, it makes no sense for them to struggle to form the world in their image. Yet, they constantly have to adapt and adjust to force the world into that image–the same one they will not admit is not what they imagine it to be.
It’s an incredible piece of characterization every time Jones tries it. Her villains want everything from a place to stay to a town to rule. Sometimes magic helps them, and sometimes magic defeats them–but no matter how much magic goes into the story, the painful reallness of the villain gives the whole thing a grounding in truth.