Hideous Creatures: Deep Ones (2013)

Publisher's blurb:

Hideous Creatures: Deep Ones dives deep into the myth of the batrachian denizens of Innsmouth. Are they human hybrids, or alien implants? Telepaths or psychopaths? Mermaids or monstrosities? From the legends of the Japanese kappa to the "kulullu" carved on the walls of Babylon, the spoor of the Deep Ones lingers everywhere.

In this series, Kenneth Hite looks at the creatures, species, and monsters of the Cthulhu Mythos from every non-Euclidean angle. Alternate versions and new explanations provide the same jolt of mythic bisociation that the gods and titans receive in the Trail of Cthulhu corebook. Hite traces these foul things through their legendary history, and provides further clues for any Investigator to follow. Horrific scenario seeds burst and bloom, story spines protrude and deform, in a blasphemous garden any Keeper can harvest.