I doubt that I will get to suggestions for every square, but it's always fun to come up with suggestions of books that I've already read and recommend for the various categories.
I am not a serious horror reader, so I am always on the lookout for books that fill the squares without being overly scary. I'm easily frightened!
So, here goes!
My first recommendation is a book that I read earlier this year: Triptych by Karin Slaughter. If you've not read Slaughter, she writes solid police procedurals. This is the first in her Will Trent series, and it's good. She employs misdirection beautifully, and surprised me three different times before the end of this book.
If you're not into modern mystery thrillers which can be legitimately gory, then I'd recommend The ABC Murders by Agatha Christie, which is one of her strongest Poirot mysteries. And Then There Were None would also qualify as a "serial killer" narrative.
Jack the Ripper is probably the most famous serial killer of all time, and Lyndsey Faye wrote a very entertaining Jack the Ripper/Sherlock Holmes mash-up called Dust and Shadow. In addition, she wrote a retelling of Jane Eyre, Jane Steele, with a main character who is a multiple murderess that both Obsidian Blue and I loved.
Who doesn't love a good ghost story? For the players who didn't read along with our group read of Ammie Come Home last year, it was pretty widely enjoyed as an old school gothic romance/ghost story from the 1960's. Barbara Michaels was an extremely prolific and accomplished writer who knew how to entertain her readers. An Inquiry Into Love And Death by Simone St. James is a more recent release in this same genre.
If you are a fan of YA lit, Maureen Johnson's The Name of the Star is the first book in her Shades of London trilogy, which is good fun. And Jackaby, which is billed as "Buffy the Vampire Slayer meets Sherlock Holmes" has a main character who is a ghost.
I also loved The Graveyard Book by Neil Gaiman when I read it last year for Halloween Bingo. It is sweet, charming and a bit harrowing - an absolutely lovely book.
There are a minimum of one million qualifying books set in London, so I'm going to mention four series that I love that are set there. First, V.E. Schwab wrote A Darker Shade of Magic, a series that is set in not one, but four, Londons: Gray London, Red London, White London and Black London. I adore this entire series. The Alex Verus series, written by Benedict Jacka and beginning with Fated, is an urban fantasy series in the vein of Harry Dresden, set in London. Ben Aaronovitch writes the beloved and well-regarded Peter Grant series, which starts with Rivers of London. This is the only one I've read, but I plan to read book two - The Moon Over Soho - for this square this time around! London Falling is the first book in the Shadow Police series by Paul Cornell, and is basically a police procedural/urban fantasy combination that is a bit more gory than the rest of the books on this list, but is very good.
Neverwhere by Neil Gaiman fits this square perfectly, if you are looking for a stand-alone, and Sherlock Holmes is nearly always a fit for this one - except for The Hound of the Baskervilles, which is set on the moors.
This square has given people a bit of trouble so far, and I only have a few identified that will fit! Uprooted by Naomi Novick is a no brainer, with a corrupted Wood featuring prominently. In the Woods by Tana French is a very good mystery. I have enjoyed all three books in her Dublin Murder Squad series, although the first one is the only one that will fit this square. In addition, Daughter of the Forest by Juliet Marillier is one of my favorite fairy tale retellings, set in the mysterious Sevenwaters Forest.
I am planning on reading Endless Night for this one - by Agatha Christie. If my memory serves me correctly, there is a folly in a woods that is integral to the story.
Please feel free to add your suggestions in the comments below!