Ms. Grunkle

Ms. Grunkle is the villainess of JumpStart Adventures 4th Grade: Haunted Island & the fourth-grade substitute teacher who turned the kids into monsters & brought them to Haunted Island, which she apparently rules over. Her appearance fits the popular depiction of a witch to a tee, with her having gray skin (although it's blue on the icon), black clothing & a pointed hat.

JumpStart Adventures 4th Grade: Haunted Island (1996)
Ms. Grunkle appears at the beginning & ending of the game as well as whenever the user enters a new room in her house. Sometime after you finish playing one of the minigames she flies by on her broomstick to taunt the user with typical villainous comments ("So, you think you're pretty good at my little games? Well, you haven't seen anything yet!") before flying off. Curiously, she is sometimes referred to as "Mrs. Grunkle," prompting one to wonder whatever became of her husband (she has a skeleton in her living room watching TV & holding a remote, which could have been her husband at one point). She does not have an explained motivation for her actions in the game.