It allows you to mark several targets with your bow before unleashing a volley of arrows that are guaranteed to hit all of them. When you read the book, you’ll unlock the Mark of Death ability (or upgrade it if you already have it).
Use the key you just picked from the pig sty, and you’ll enter a small room with a shining pedestal.
Drop down and follow the tunnel, and you’ll soon hit a locked door. Shoot the hook holding the net with an arrow, and it’ll drop down, opening a hole leading to the cellar. Once you have the key, turn around and you’ll see a big pile of stuff hanging in a net.
