So, my kid and his friends are currently obsessed with the Slender Man myth. I got him a simple iOS game and he played the heck out of it, and he was wanting one for his PC.
I’m pretty sure there’s at least 2 Slender Man games out there, but you do the same thing in each of them - run around and collect notebook pages until he pops out of nowhere and grabs you. I think one is based in a school while one is in the woods…
There are a couplebeingworked on now that are on Steam Greenlight but not yet released. If your son just likes the jumpy scary, then he should check out SCP-087 (write up) and SCP Containment Breach, both of which are also based on internet created horror (there’s actually a term for that called “creepypasta”. How dumb is that?). SCP-087 is basically a terror inducer, not really a game. There’s always Amnesia: Dark Descent, too, which will scare the pants off any person.