Design a horror game: What's your setting, monster, and mechanic?

[Shortie]

Have you ever thought about designing your own horror game? If you have, what ideas have you come up with and even what story have you come up with for your very own horror game?

If you could design a horror game, what would your setting be, mechanics be like and what kind of monsters would you add to your game? 

[killamch89]

Setting: A sprawling Japanese apartment complex during a heatwave. Monster: The building itself, gradually changing its layout and absorbing residents. Mechanic: Heat management where staying cool preserves sanity, but air conditioned areas slowly become organic and dangerous.