If you are looking for unique ideas, I'd suggest a horror game that doesn't try to immerse you so well that you're scared even though you aren't in danger in real life. Instead, go for fourth wall breaking horror, where the gameplay isn't so much about survival but how messed up it is.
A few examples:
Some people get so scared by jump scares/the atmosphere that they pause the game. Use this to your advantage by having a jumpscare AFTER they're the game has stopped.
Do something original with the thing you're running from. Maybe it causes the game to lag when you get near it. Maybe you can only HEAR where it is. Maybe you have to TURN OFF YOUR MONITOR or HEADPHONES to prevent seeing its eyes or hearing the bloodcurdling scream that causes death. Maybe it only moves when you move. Maybe it freezes while you're looking at it. Maybe it looks like a distorted version of the player. Maybe you enter zero gravity near it.
Jumpscare during an item collection cutscene/immediately after respawning.
Respawn the player somewhere they've never been when they die, so they not only feel lost but also have no idea where they are or how they got there.
Have the flashlight do something very, very weird. Naturally it will drain battery power over time. Yes, it increases tension, but it also doesn't lend itself to the supernatural very well. Maybe battery power actually INCREASES when you're close to death. Maybe the flashlight is distorted by the creature. Maybe the creature also has trouble seeing in the dark, and can only find you when you're using the flashlight, and can only hear you when you're nearby and moving. Maybe, instead of a flashlight, the creature produces light and whatever the current flashlight button is instead lets you see through the eyes of the creature.
Another suggestion: have absolutely NO jumpscares, or scares of any kind, until after the player has found all the items they think are required to win. THEN spawn the creature. They're probably so tense by that point they almost WANT to be found.
Have elements of permadeath- lose something (items/money/whatever) whenever you die but allow the player to get it back if they can return to it.
Floating things are creepy. Flickering lights are creepy. Sounds playing BACKWARDS are creepy. Video game glitches *can be* creepy if you aren't the one who found them. Complete darkness is extremely scary, but nobody seems to do blinding light. Having to solve puzzles while something's tracking you is creepy.
I've actually only ever tried 1 horror game but I've played enough creepy games (mostly Metroidvanias

) to know what makes me jump. Basically go for the unexpected, but do it in a way that no other horror game has- pure jumpscares do not good horror make.

Boo!
