Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Slender
After the sixth page, Slender Man becomes much, much more persistent.
Page 6? Try page 4.
Forget the Slender Man. This game will ignite the Primal Fear of the darkness in you.
Combine that with the thunderous noise echoing louder and louder as you get more pages of Alex Krailie's notebook is guaranteed to induce paranoia.
A meta example. This game was scary enough to scare TOM of Toonami. The same TOM who has dealt with giant aliens blobs and insane computer viruses.
On his personal blog, Troy Wagner confessed to having ripped off his headphones in fright while playing Slender. That's right: the guy who helped create one of the cornerstones of the mythos—the very series that inspired the game to begin with—was frightened by this game.