Gothic characters like Count Orlok in Nosferatu and the Other Mother in Coraline are so scary because the combination of familiarity and strangeness in them raises the level of their unexpectedness. Let's look at this in more detail.

At the beginning of the film, Count Orlok is supposed to be doing something as ordinary as buying a house. This is why Hutter goes to meet him. He is certainly not expecting what he finds, nor is he expecting the Count to want to suck out his blood when he cuts his finger. Yet Hutter stays and goes through with the real estate deal. He is already getting the idea, though, that there is more to Count Orlok than an interest in property. As the terror mounts, the familiarity lessens, and the Count behaves more and more threateningly. Hutter, of course, never expects any of this when he first goes to meet the Count and the horror is increased by this unexpectedness. Hutter thinks that he is just doing his job. He has no idea that he is meeting a vampire.

In Coraline, there is also a terrifying character who has enough familiarity to make her horror unexpected. This is the Other Mother whom Coraline meets when she goes through the strange door. The Other Mother begins by treating Coraline well and giving her a good lunch and toys. The Other Mother looks something like Coraline's real mother, but here is where the familiarity stops. The Other Mother has black buttons for eyes. Coraline has entered into a new world of unexpectedness, and things become terrifying quite quickly when Coraline is disturbed by the strangeness of the other world and then by the realization that her real parents have been kidnapped by the Other Mother. The Other Mother's frightfulness is increased because we never find out exactly who or what she is even after Coraline defeats her and rescues her parents.