THE HOUR OF MEETING EVIL SPIRITS:
An Encyclopedia of Mononoke and Magic (Yokai Book 2)
by Matthew Meyer (yokai.com)
Want to learn about Tesso the Iron Rat?
How about the ghosts of vengeance known as the Goryō?
While Meyer has a lot of the content from this book and the first in the series up on his website, it is totally worth owning the paperback.
Here's an example of his illustrations...
TRANSLATION: living ghost
ALTERNATE NAMES: shōryō, seirei, ikisudama
HABITAT: inhabited areas
DIET: none; lives off its owner’s emotions