Sandy Petersen's Cthulhu Mythos: Pathfinder
Sandy Petersen's Cthulhu Mythos is the most comprehensive guide to including Lovecraftian elements in your Pathfinder Roleplaying game¸ written by the author of the groundbreaking Call of Cthulhu RPG¸ and developed primarily by James Jacobs (creative director of Paizo) and David N. Ross.
This massive 512 page tome contains over 100 monster stat blocks¸ dozens of which are Cthulhu Mythos monsters that have never been described for Pathfinder - including new rules for interacting with 25 different Great Old Ones and Outer Gods (they are much more than a simple encounter!).
This tome is much more than a mere bestiary¸ however. Inside you will find new rules for Insanity and Dreams; 40 new spells and 30 Rituals - a new magic ruleset; dozens of mythos items and artifacts; dozens of Mythos cults detailed; and four new player races from Lovecraft's universe - Dreamlands Cats¸ Mythos Ghouls¸ Gnorri¸ and Zoogs - as well as new character options¸ professions¸ feats¸ and race options for them.
If you like Cthulhu¸ Pathfinder¸ Monsters¸ and Madness¸ you need this book!