[The King in Yellow](https://en.wikipedia.org/wiki/The_King_in_Yellow)
Perhaps one of the best works in American fiction in terms of supernatural horror, the King in Yellow is a public domain book of short stories, where multiple stories are connected by a play called_ The King in Yellow_. Anyone who reads the play is doomed to madness and despair, but more importantly, anyone who reads it becomes aware of the King, and the King becomes aware of the reader. I'll leave a small passage here from the Yellow Sign, a short story in the book:
_"The gate below opened and shut, and I crept shaking to my door and bolted it, but I knew no bolts, no locks, could keep that creature out who was coming for the Yellow Sign. And now I heard him moving very softly along the hall. Now he was at the door, and the bolts rotted at his touch. Now he had entered. With eyes starting from my head I peered into the darkness, but when he came into the room I did not see him. It was only when I felt him envelope me in his cold soft grasp that I cried out and struggled with deadly fury, but my hands were useless ... I knew that the King in Yellow had opened his tattered mantle and there was only God to cry to now."_
If you want to make Fiddlesticks the scariest guy on the rift, you need to use the strongest and most potent kind of fear there is- fear of the unknown. Before Stephen King, before Lovecraft, Robert W. Chambers created the original in eldritch horrors, the Mac Daddy of them all, the King in Yellow. If you want to set the mood for designing new Fiddlesticks, to get some inspiration, I highly suggest reading this book.