Malleus Monstrorum: Cthulhu Mythos Bestiary - Rules of Play says:
The information within is designed to bring the creatures and bizarre races of the Cthulhu Mythos to life at the gaming table, as well as all manner of Great Old Ones, Outer Gods, Elder Gods, Avatars, and Unique Beings. Their lore and statistics updated and revised for the Call of Cthulhu 7th edition game (and Pulp Cthulhu). All brought to startling life by the illustrations of expert artist Loïc Muzy. This two-volume collection is packed with ideas, concepts, and insights to immerse your scenarios and campaigns deep in the heart of the Cthulhu Mythos.