The best horror movie villains aren't supernatural monsters, because the villains of the natural world are always more frightening than those of the supernatural world. The reason for this is relatability—a major element of what makes horror movie villains frightening. The relatability of any given horror movie villain is subjective; no single villain can be completely relatable to everyone. However, without some amount of relatability, horror movie villains would lose their ability to frighten anyone. In other words, if a horror movie villain becomes so supernatural and alien that it becomes impossible to understand it even on a most basic level, it loses its capacity to strike fear in people's hearts. If that same horror movie villain were to somehow become more relatable, its frightfulness would increase. Essentially, the more relatable a horror movie villain is, the more frightening it has the potential to be.
Audiences can more easily relate to horror movie villains who are somehow connected to mundane human experiences, such as going to the supermarket, getting the mail, or taking out the garbage. For the most part, these experiences do not contain supernatural elements. That is not to say that human experiences cannot or do not have supernatural elements. Many religious and spiritual belief systems include the supernatural by default, and even atheists can believe in ghosts. It is also not to say that all highly relatable horror movie villains are frightening. It just means that, for any given horror movie villain, the more relatable it is, the more horrifying it can be. The success of a horror movie villain is directly proportional to, but not guaranteed by, its relatability. In other words, highly relatable horror movie villains can also lack frightfulness.
It's important to note that almost any fictional monster can fit into the category of supernatural monster. Arguably, the term supernatural monster usually refers to creatures from or related to the afterlife, such as vampires, the undead, ghosts, and demons. In today's horror movies, the category of supernatural monster doesn't have to be so limited, and can include Lovecraftian monsters like Cthulhu, science fiction monsters like the Alien franchise's Xenomorph, and fantastic monsters like Smaug in The Hobbit. The main element that differentiates a supernatural monster from a natural monster is that the natural monster exists in the real world. A natural monster could be a human, an animal, bacteria, etc. Furthermore, horror movie villains aren't required to be monsters (i.e. evil, cruel, etc.), but the villain's role as antagonist usually entails being a monster on some level.
Why Supernatural Horror Movie Villains Are Less Scary
The best horror movie villains are those who audiences can relate to, but more importantly, they are the villains that audiences can imagine in their own lives. Relatability makes the scares more effective and more efficiently preys upon fears. Relatability is also one of the reasons why authors often combine supernatural horrors with mundane objects or insert supernatural elements into aspects of everyday life. Adding a natural element to a supernatural horror movie can help to encourage the audience's suspension of disbelief by grounding the supernatural elements in reality. When a movie is more grounded in reality (i.e. more natural), the audience can better place themselves in a character's shoes and consequently experience their horrors more deeply and authentically. That doesn't mean that supernatural horror movie villains aren't frightening. It simply means that supernatural elements act as an extra layer of removal between the horror movie villain and its audience.
For example, the Xenomorph of the Alien franchise is probably one of the most frightening, disturbing, and iconic villains and supernatural monsters in horror movies. The Xenomorph is so frightening because it taps into many human fears with its appearance, life cycle, and most importantly, its penchant for killing humans. However, because it would be unlikely for Alien's Xenomorph to show up in the audience's own life, the real fears associated with the creature are diminished. Likewise, the Thing in John Carpenter's The Thing is one of horror's most unforgettably terrifying villains because it taps into some very human fears in some very specific ways. However, even in the context of the movie, the Thing is usually restricted to Antarctica, which, like its relative lack of relatability, makes the likelihood of encountering anything like it in real life a distant impossibility.
The Best Horror Movie Villains Don't Need The Supernatural
Horror movie villains that aren't supernatural are more relatable and therefore more frightening. An excellent example of this is in The Shining, where Jack Torrance is the main villain. The Overlook Hotel is also a villain, but ultimately, it is Jack who decides to attempt a murder spree—the hotel is just inspiration. Jack is flawed, a recovering alcoholic, and a violent and abusive husband and father. Although he is goaded on by supernatural monsters in the hotel, he is the natural monster of the movie, and the one that his family fears most. Jack Nicholson's Jack has become a horror icon and, quite literally, the face of the franchise. A character like Jack—unlike the Xenomorph or the Thing—could very well be living next door or worse, under the same roof. This relatability is what makes him linger in the mind as a horror movie villain.
In Blood Quantum, arguably the best horror movie of the 21st century, the villain is a mix between supernatural monster and natural monster. The movie's premise is that white people are being transformed into flesh-eating, undead monsters for an unknown reason, though it's likely due to pollution of local water resources. All the white people, alive or undead, are dying to get into a First Nations reservation rumored to have a cure, literally the blood of the First Nations people. Therefore, the white people in the movie have an insatiable need for the blood of the First Nations people both as zombies and as humans. What makes the villain of Blood Quantum so relatable is that it is drawn from history. The natural monsters that the First Nations face in the movie are real, and their supernatural zombie is almost incidental.
In The Invisible Man, the villain is purely a natural monster (Adrian, the ex-boyfriend, to be precise), but one that uses a supernatural disguise (almost à la Scooby-Doo) to attack his victim. The movie starts out by implying that Cecilia is either losing her mind or actually seeing ghosts. While the movie pushes all the right buttons in this respect to create some frightening scenes, the biggest frights occur when it turns out that Adrian is alive and has been manipulating Cecilia with technology. The relatability in this instance really enhances the villain because it has become frightfully easy to manipulate people with technology in real life. It is very easy to imagine Adrian as someone's manipulative boyfriend, and his supernatural disguise actually diminishes how scary his character really is.
The Shining's Jack Torrance, Blood Quantum's white people, and The Invisible Man's Adrian show how the best horror movie villains are not supernatural monsters and instead are very much human. Looked at in this way, supernatural elements can add flavor and layers to a horror movie villain, but in the end, the scariest villains are always those that reflect the audience's own image of itself. The closer that reflection comes to portraying real life, the scarier it ultimately is.