Mrs. Gorf is the closest thing this book has to a villain, although she's not much of a factor for twenty-eight out of the book's thirty stories. She has "a long tongue and pointed ears," and was "the meanest teacher in Wayside School" (1.1). Her favorite pastime is wiggling her ears, sticking out her tongue, and turning kids into apples, and she does this so many times in the first chapter that she has almost no kids left. She's so nasty that it's hard to tell why she might have become a teacher in the first place. Maybe she was just running low on apples?
Mrs. Gorf's reign of terror comes to an unexpected end when Jenny holds up a mirror in front of her, causing Mrs. Gorf to turn herself into an apple. Louis unknowingly eats her, and that's the last we see of Mrs. Gorf until she returns as a ghost in the twenty-ninth chapter, menacing the kids on Halloween with threats of permanent apple transformations. Not even the beloved Mrs. Jewls can banish her.
But the ghost of Mrs. Gorf doesn't handle kindness very well, so when Stephen tries to hug her, she disappears. Thankfully Mrs. Gorf, in ghost or human form, doesn't seem to be a lasting threat to the kids on the thirtieth floor. And if she ever comes back, they can pretty much kill her with kindness.