The Blair Witch Project.
Words cannot summate just how excited I am. I have always considered the original Blair Witch Project to be the second scariest movie I have ever seen (coming in behind The Exorcist of course). I also really dug the sequel for its tone and pragmatic "we already did that now let's do the exact opposite" approach. And now, well, from what we're hearing after the press viewing, 2016's Blair Witch may enter into the upper echelons of that 'scariest flicks of all time" list.
Also worth embedding is the teaser for The Woods, simply for juxtaposition and, well, I really dig the way they used this version of Every Breath You Take.