This post has been updated to include links to all of the relevant booklists!
Ghost stories: any story involving ghosts or hauntings, including haunted houses, buildings, graveyards, etc.
Book suggestions: Jackaby by William Ritter, The Little Stranger by Sarah Waters, The Turn of the Screw by Henry James, and The Ghost of Sparrow Hill Road by Seanan McGuire. In addition, this is a recycled category, so there's already a list for it - Ghost Stories and Haunted Houses.
13: any book that relates to bad luck, superstitions, including (but not limited to) black cats, ravens or crows, or the unlucky number 13, either in the title, series, book cover or page count.
Book suggestions: Okay, I totally love this new category! The Thirteenth Tale by Diane Setterfield, The Thirteen Problems by Agatha Christie, The Raven Boys by Maggie Stiefvater, We Have Always Lived in the Castle by Shirley Jackson (the Penguin Classics Deluxe edition, which I own, has a black cat on the cover. See link), any of the books from A Series of Unfortunate Events (the series ended on the unlucky 13th book). Also check out MBD's Black Cat list, and the new 13 list!
A Grimm Tale: any fairy tale or retelling of fairy tales, folklore, legends, etc.
Book suggestions: There are a lot of really good retellings out there! However, a few that I have either enjoyed or heard good things about include: The Bloody Chamber and Other Stories by Angela Carter (I haven't read this one, but OB really liked it), The Bear and the Nightingale by Katherine Arden (based on the Russian fairytale Vasilia the Beautiful), Wildwood Dancing by Juliet Marillier (she has a number of good retellings). See the new list: A Grimm Tale.
Relics and Curiosities: concerning magical, supernatural or haunted objects, such as spellbooks, talismans or swords.
Book suggestions: The Book of Lost Things by John Connolly, Relic by Douglas Preston, The Lost Book of the Grail by Charlie Lovett, Harry Potter and the Sorcerer's Stone by J.K. Rowling. There's a list for this square, too: Relics and Curiosities!
Deadlands: elements of the undead - zombies, wights, vampires and other revenants.
Book suggestions: Ghostwalkers (Deadlands #1) by Jonathan Mayberry, The Girl with All the Gifts by M.R. Carey, Hotel Transylvania by Chelsea Quinn Yarbro, Anno Dracula by Kim Newman. In addition, there is a list for zombies: Deadlands, and the vampire books on MBD's list Vampires.