My go to for one-shot Horror is Dead of Night, so if you want to do it episodic (each session like an episode of the show with different characters as the hapless victims), that would be the way to go. I've found it works well at emulating TV or film based horror and is a relatively simple system, while rewarding tropes, so is great for giving breathing room for folk to ham it up.
Key features:
Survival Points - like luck, hit points, plot resources, rerolls and all sorts bundled together - while you still have some, you've got a level of plot immunity, once out your doom is imminent...
Bad Habits - playing into horror tropes gets you SP back "I'll just go check on what that screaming was on deck by myself"
Tension - as things get worse tension die (get a bit d20) racks up - the world gets more dark and horrifying as it clocks up. The ref can use tension points to mess with player's rolls.
Baddies can be esoteric and tough - they've got their own rules, so the unknown quality of Dracula (or whoever's) powers can be fearsome.
Potential downside:
It is meant to be horror-fuelled and so campaign play is not really font and centre. If your players want the same character for many weeks, this isn't really the game for that.
I've not tried it myself yet, but I've heard good things about A Town Called Malice (Monkeyfun Studios) might fit as a kind of Nordic Noir spin on things with an "unknown" baddie - although again, it strikes me as one shot material.