Pathfinder: Horror Adventures is a sourcebook that occupies a somewhat strange place amongst other sourcebooks. Horror Adventures modifies existing Pathfinder systems or creates entirely new systems in order to provide the basis for a horror-themed campaign. Curses, insanity, torture, hauntings, and other similar events are all given a place here. This definitely allows for the creation of a terrifying campaign, but the systems’ reliance on one another it makes it difficult to incorporate many of these ideas into any existing campaigns you may already be running.
For the uninitiated, Pathfinder is a pen-and-paper RPG based on the 3rd edition rules of Dungeons & Dragons. Typically, adventures take place in traditional fantasy settings. Oftentimes, elements of horror, such as the black magic, necromancy, or hauntings can make appearances. These elements are just part of the larger story, and your party will often act towards an army of bloody skeletons as they would any other enemy. In Horror Adventures, that army of skeletons will have much more of an impact than just reducing your hit points.
A huge change to Pathfinder in the Horror Adventures book is how all these terrifying encounters impact your party psychologically. In a way, Horror Adventures seems somewhat like a response to a game like Darkest Dungeon, where fear, stress, and madness are even greater threats than swords. There are now in-depth systems for fear and sanity which can greatly impact your saving throws, combat effectiveness, and can even have permanent scarring effects on your characters. Many of the new spells, feats, and equipment included in the sourcebook plays off of these systems directly, which can make it difficult to incorporate some of these new options into existing characters and campaigns. Horrific diseases, afflictions like possession and lycanthropy, madness, hauntings, even fleshwarping body horror all make appearances to provide horror options.
Horror Adventures does not limit these new options to one style of horror. It gives GMs and players alike tons of options to create any type of horror scenario or characters they would like. Want to recreate the gothic horror of Edgar Allan Poe? Challenge the Old Gods of H.P. Lovecraft? Save a town from a seemingly unkillable, hockey-mask wearing foe? All of these scenarios can be brought to life. There are a huge number of character archetypes to transpose existing classes to a horror setting. Some, like the blood alchemist (who uses the blood of slain foes as the base for their alchemist abilities) could fit into regular campaigns with a little fancy storytelling. Others, like the gingerbread witch (who can literally just swallow her enemies at a certain level) don’t make as much sense in a typical adventuring party and would probably be a bit out of place journeying alongside a human paladin and a half-orc barbarian.
The new feats in Horror Adventures are mostly tied in with the new systems, and will thus only see much use in a designated horror campaign. Most of the spells could find their way into a non-horror campaign, although many are somewhat based on existing spells but given a horror makeover. Since so much of the fun of tabletop RPGs like Pathfinder lies in the storytelling element, much of what is included in Horror Adventures stylistically does not mesh that well with existing campaigns. But, if a horror-themed campaign is what you want to do, this book will cover pretty much any direction you want to try that from.
One element that works very well with existing campaigns are some of the new items. For the most part, they do not rely too heavily on the fear and sanity systems that Horror Adventures focuses on. Several of these items could be utilized to add some better frightening elements (the new torture items could make for some fascinating interrogation scenes) or to create unique scenarios to surprise players. For example, a new item called the “needful doll” got my gears turning. Picking it up triggers a curse that can cause terrible nightmares in its owner. Naturally, any attempt to get rid of the doll without meeting certain criteria will result in it appearing right back with you when you least expect it. An item like that does not need to be confined to a purely horrific campaign, but can sprinkle in some of those elements of horror without completely entering that realm.
Overall, Pathfinder: Horror Adventures brings some seriously interesting elements to the RPG. It is not an absolute “must own” sourcebook, like Ultimate Equipment, the Advanced Player’s Guide, or some of the various codexes, but it does provide the basis for a fresh take on your Pathfinder campaigns. If you’re looking to start a brand new campaign with a bit more of a horror twist, this is your book. If you’re looking to add a bit more spice into your existing campaign and turn things a bit darker, it would be a solid addition. If your Pathfinder budget is limited and your already in the middle of your high-fantasy campaign, Horror Adventures can probably stay in the crypt.