When I was growing up the two that scared me most were Jafar and Ursula. Jafar scared me so much that I literally hated to watch Aladdin. Everything about him was so creepy especially when he turned into the huge snake.
Frollo because of what he does to Quasemodo to make him feel worthless and he mentally destroys Quasemodo it makes me cringe at how evil and black hearted he is