From publisher blurb:
Welcome to the Rise of the Goblinoids, the fourth in our line of Monster Menagerie monster books. Each volume in this line presents a small set of monsters tied to a single theme, but spread over a range of CRs. For Rise of the Goblinoids, that theme is goblins and all the strange things descended from one of the most prolific of monstrous species. In addition to goblins who have taken to the trees, or who patrol the oceans, we have goblinoids that have mixed with genies, demons, and the forces of nature.
This collection can be helpful to GMs in many different ways. Goblins form the backbone of many of a campaign's early adventures, but after a CR 2 bugbear is no longer a threat (or at least after 12 of them aren't), most groups move on to dragons and giants, leaving goblinoids behind. Not only is this unfortunate from a stylistic point of view, it's annoying for rangers who take humanoid (goblinoid) as a favored enemy, wizards who craft goblin-bane weapons, and any character who has a hatred of goblins as part of a character background. With the goblinoids in this book, a GM can extend the goblin-bashing phase of a game well into the upper levels.
Additionally, the book can help create a campaign arc: a literal rise of the goblinoids. Perhaps many of the new races presented here are being seen for the first time, and their evils big and small are now spreading across the known world. Why are oni in goblin forms banding together? What has driven hidden goblin subraces out of their islands, forests, and underground caves? Whatever is causing it, the heroes had better put an end to it before the rising tide of goblinoids washes civilization off the face of the world!
However you choose to terrorize your players, we're hopeful you'll find something useful in our fourth Monster Menagerie. Now, ready yourself for the front wave of the Rise; the pucks are hammering out weapons for an átahsaia's new army, ponaturi are screaming war chants on the beach, and the ophidiyarr have unearthed devices mortals were never meant to find!