From publisher blurb:
Ancestries of Tombstone presents the Chupacabra Ancestry for your Pathfinder Second Edition games.
What is Tombstone?
The practical answer is that Tombstone is a campaign setting for Pathfinder Second Edition. This means that you need the Pathfinder Core Rulebook (Second Edition) to play games in the world of Tombstone.
A more interesting answer is that Tombstone is a gritty alternate history wild west setting with elements of anime, fantasy, and gothic horror. The year is 1871 and the world is full of monsters and magic but it diverges from traditional fantasy settings in a number of ways. First of all, the world of Tombstone is our earth, or at least an alternate version of it. This allows us to assume a baseline of actual history – for example, the city of Las Vegas, Nevada won’t be founded until 1905 – except for the details that are called out as being different. Secondly, the ancestries of Tombstone are not the ones found in traditional fantasy settings. There are no elves, dwarves, gnomes or halflings in the world of Tombstone. Instead, humans live alongside centaurs, jackalopes, rougarou and the secretive chupacabra.
Magic has always existed but was much less common and much less powerful until the summer solstice of 1847 saw a surge of magical power unheard of since the time of King Artur. Since then, instead of quickly falling back to normal levels as is expected with magical spikes, magical power levels have been slowly but steadily building. Magical scholars have taken to calling this event the Resurgence.
The Southwestern Territories are also facing a new threat in the form of The Blighted. A shooting star landed in the barren wastes of West Texas and now strange mutants are coming out of the desert...