WARNING: The following discusses details of the plot, characters, encounters and events of the Adventure Path Pathfinder: Rise of the Runelords #1. Do not read further if you intend to play as a PC in this Adventure Path.
Serious spoilers follow.
I can identify quite a few antagonists in this first adventure, which is something that surprised me when I gave it an initial read. In general, when reading an adventure, I expect to find a Big Bad, a henchmen or two, and the collection of mooks that are speed bumps between the party and the Big Bad. Going through "Burnt Offerings", there are a couple Big Bads, more than a few henchmen who have their own plots and motivations, and even a couple mooks who are active opponents for the party.
This is the ultimate big bad of the Adventure Path, but his involvement in this first chapter is limited to actions behind the scenes and in the background that kick off the events. Karzoug, once the Runelord of Greed, is looking to regain the magical and secular power he once held thousands of years ago as a Runelord. His method is to power up a runewell with the souls of greedy people, but in the process, he has triggered the magical qualities of other runewells, which has set into motion the events of "Burnt Offerings".
What does the Bad Guy want? Karzoug wants to regain his power and resume ruling as the Runelord of Greed where he left off thousands of years ago. That is about all we learn about him and his motivations in the first adventure.
What does the Bad Guy do? However, despite being the Big Bad of the overall Adventure Path, what he wants really has no play in this first adventure. The events of this first scenario are an unintended accident of Karzoug's overall plan, and Karzoug is entirely a passive force in this adventure.
What if the PCs do not stop the Bad Guy? The PCs will not be around to stop Karzoug from reclaiming his power and, ultimately, his lost throne.
In "Burnt Offerings", Nualia is one of three Big Bad's that the PCs may encounter. Nualia is an Aasimar who has fallen into the thrall of the goddess Lamashtu, and functions as an example of the Sin of Wrath. When the adventure starts, Nualia has already become a worshipper of Lamashtu, killed her stepfather, burned down the church in Sandpoint, gotten revenge on her ex-lover and taken control of the goblin tribe of Thistletop. Whew. That is a busy back-story,
What does the Bad Guy want? Nualia wants revenge now on the people of Sandpoint for having treated her like an object, rather than a young woman. At the urging of her goddess, when the adventure begins she is trying to free a barghest who, she hopes, will help her destroy the town.
What does the Bad Guy do? Nualia triggers the first encounter of adventure by sending Tsuto to recover the remains of her stepfather from the Sandpoint cemetery. After that, she does not do much more that actively affects the PCs. In the period of the adventure, she is trying to find Malfeshnekor, the barghest, to free him and unleash him on Sandpoint.
What if the PCs do not stop the Bad Guy? Nualia will eventually find and free Malfeshnekor, and will lead her goblin army in an assault on the town of Sandpoint looking to wreak havoc and kill everyone she finds. With the barghest's help, she will purge the celestial from her body and become a full demon. Her wrath fed by Lamashtu, she will grow into a powerful force of evil in the region, hunting down and killing anyone she feels has done her wrong. Ultimately, this might include her celestial father.
Tsuto is the most active opponent for the PCs, and his actions lead the PCs to the adventure. Yet he does not really qualify as a Big Bad, because he is working for Nualia as a henchman. He is the 2nd villain of the piece, pursuing his agenda in the large context of his boss's goals. Tsuto is the hidden agent behind the first encounter and attack on Sandpoint, having blackmailed his stepfather into helping smuggle goblins into the town. It is his pursuit of his own revenge in Part 3 which attracts the attention of the PCs and gives them all the clues they need to lead them to his mistress, Nualia. If not for Tsuto, Nualia would likely be able to proceed with her plans in peace.
What does the Bad Guy want? Tsuto is an outcast from his family and, like Nualia, is seeking revenge for slights he feels his stepfather has done him. He wants his stepfather dead and his sister to accept and join him. However, Tsuto has a second motivation – his lust for Nualia, which drives him to do as she commands. It also leads him to pursue his own revenge, to impress her, and thus leads to her downfall.
What does the Bad Guy do? Tsuto arranges for the smuggling of goblins into the town for the Part 1 attack on Sandpoint. He also leads the party of goblins that digs up the remains of Nualia's stepfather so she can sacrifice them to her goddess. He then kills his stepfather, kills the employees of the Glass factory, and kidnaps his sister with the goblins help – all of which ultimately should lead the PCs to Nualia's lair with the Thistletop goblin tribe.
What if the PCs do not stop the Bad Guy? If the PCs do not get involved, Tsuto will end up returning to Nualia with his sister. His sister will become another sacrifice to Lamashtu, and Tsuto will become even more dedicated to Nualia.
In part 2, I'll look at the remaining Bad Guys.