Sandy Peterson's Cthulu Mythos (5E)

Sandy Petersen's Cthulhu Mythos is the most comprehensive guide to including Lovecraftian elements in your Roleplaying game, written by the author of the groundbreaking Call of Cthulhu role-playing game, and developed primarily by James Jacobs (creative director of Paizo) and David N. Ross. This massive tome contains over 100 monster stat blocks, dozens of which are Cthulhu Mythos monsters that have never been described for Dungeons and Dragons 5e - including new rules for interacting with 25 different Great Old Ones and Outer Gods (they are much more than a simple encounter!).