From the Kickstarter description:

Mythos Monsters is a 72-page full-color softcover 5E bestiary featuring over 40 fantastical beasts drawn from and inspired by the writings of H.P. Lovecraft and August Derleth. These dream-haunting, sanity-devouring masters of madness and their murderous minions have haunted the pages of games like Dungeons and Dragons and Call of Cthulhu since the earliest days of RPGs, and within these pages you'll find a ton of terrific terror to unleash upon your unsuspecting players!