When the Hurly-Burly's Done
So: witches! I feel like a lot of witches in middle-grade stories tend to be basically humans with magical powers. Sometimes the story is told from the perspective of the witch (like "Kiki's Delivery Service"); sometimes the witch is a kindly figure who helps out the protagonists (Morgan Le Fay in the "Magic Treehouse" series - possibly she's a sorceress, but I'm not sure there's a difference for this purpose). If the witch is the villain, she's more likely to be non-human, but she's still got pretty understandable, human motivations: take over the kingdom, get revenge for something, etc. There are a lot of good stories there! But what I don't feel like I see enough of is incomprehensible witches. Witches that are like some kind of weird, mysterious force of nature, doing things for their own reasons that aren't necessarily explained to the audience. Like in "Macbeth" - why are the witches wandering about on the heath y