This is a topic all about what you think would be good for a horror game.
Some of mine:
If you are going to do a co-op game, to reduce the whole 'at least I got my buddies' kind of thing give each player (or only one unlucky player) hallucinations which vary from moving shadows all the way to when he looks back at one of his friends he sees that they are scary monsters as well. (Or just use sanity points, an extremely good concept that should be used more often IMO)
When you die and go back to a checkpoint, change up a few things. Maybe move some things around, even if it just makes the player say "I don't remember this being here before"
So have some fun thinking up of good horror ideas.
Some of mine:
If you are going to do a co-op game, to reduce the whole 'at least I got my buddies' kind of thing give each player (or only one unlucky player) hallucinations which vary from moving shadows all the way to when he looks back at one of his friends he sees that they are scary monsters as well. (Or just use sanity points, an extremely good concept that should be used more often IMO)
When you die and go back to a checkpoint, change up a few things. Maybe move some things around, even if it just makes the player say "I don't remember this being here before"
So have some fun thinking up of good horror ideas.