So I asked the folks over at the DW tavern: if there was an existing playbook. Someone suggested a compendium class. Surprisingly among the more helpful responses was "Just do it". They're also where I found out it was called a Fisher King in the first place. A very short conversation, and a cursory glance at DW Perilous Wilds and I got the idea that the book could almost write itself. I was basically right.