3. The Gatherers (Amnesia: The Dark Descent)
To be fair, pretty much any enemy from Amnesia: The Dark Descent could have made it onto this list, but The Gatherers are easily the most frightening of the lot. If ending up stuck in an old, 18th century mansion with no memory of how you got there wasn't bad enough, you'll have to contend with these things; a group of grotesque monsters who stalk you throughout the grounds, emitting a spine-tingling growl as they move near. Unlike every other game on this list, Amnesia does not give the player the means to defend themselves; all you can do is flee or hide from the enemies, and that's what truly distinguishes it from a typical haunted house-type affair. A masterclass of intensity, Amnesia begins fairly innocuously but becomes more and more terrifying as it bounds along, such that by the later portions of the game, these creatures will - like several of the above enemies - smash their way through doors to get to you. Truly, it's a game that can make you lose sleep, especially if you make the ill-advised decision to play it at 2am with surround sound headphones on.