In The Forest chapter, during the waning moon (the one on the right), if you go right from start you’ll see a coffin. The goal here is to fit all of the body parts back into the coffin without any overlap in the grid squares. There are multiple solutions to this one, so it’s not necessary to put them in the same spots they are in the picture.
Video of this puzzle can be seen here: Coffin Puzzle on Youtube
The reward for completing this puzzle is a doll that used in a puzzle during the waxing moon setting.