From publisher blurb:
Welcome to Threats From Beyond, the twelfth in our line of Monster Menagerie bestiaries. Each volume in this line presents a small set of monsters tied to a single theme, but spread over a range of CRs. For the Threats From Beyond, that theme is outsiders. Rather than just present another set of pitchfork-toting fiends, author Sam Hing has put together an awesome set of outsider oddities to fill the corners and crevices of your extraplanar encounters.
The idea of Threats From Beyond is to expand a campaign’s option for outsider encounters, since anything as vast as other planes of existence should have vast and varied creatures dwelling within them. In many cases these threats can be easily added to traditional plotlines centered on devils or demons, but a few other plots can also be presented using these outsider entities. When dealing with creatures as alien as natives to another plane not all the threats come from a desire to do evil (through a prismatic couatl can certainly make life difficult for the agents of a kingdom that prides itself on law-and-order), nor are they all things players are most likely to encounters in combat (though a shax’s presence in a village may result in more casualties than an open fight).
Your players may have a handle on brigands, dragons, and other foes they can understand, but things just took a turn for the cosmic. The black chargers are lining up for a cavalry charge, the karkinides have begun to swarm, and there’s very little time left to cut a deal with a traveler to make good your escape. It’s time to deal with the Threats From Beyond!