Exist so many horror videogames that people love, like Resident Evil or Sillent Hill for example. But how do they create fear in the player's mind? You can simply put a lot of dark areas and jumpscares but those things are pretty cheap. There are many other options to made your game scary. 1-Anticipation: If you have a villainor somethong else that try to kill your character, you can build up it's arrive. For example you can put te sound of it's steps to alert the player or show him the leftovers of monster actions. That will made him rememer it. 2-Enviroment: You can push darkness, of course but also add a unsetling music or even cut the sound suddenly and make the zone look like a safe place. That will put the player in suspense. 3-Mystery: If the menace's nature is unknown to the player it may be scarier. This is because people can fell uncomfortable about unkown and strange things. But don't leave it as a total mystery. Deliver a few clues about the menace. It can turn the situation even scarier.