There is simply no way I can do justice to Pazuzu in one sitting. This is a being who’s been in fantasy gaming since the original Monster Manual II, who even managed to sneak into demon-phobic 2e, who got the full “Demonomicon of Iggwilv” workup in Dragon Magazine, and who hails from our own world courtesy of Assyrian and Babylonian mythology (not to mention The Exorcist). He’s been part of Pathfinder since pretty much Day One as Lamashtu’s foil, and he’s the most powerful demon lord (at CR 30, topping even mighty Dagon) in Bestiary 4. He doesn't deserve a blog post; he deserves a sourcebook.
That said, here are three quick highlights to remember when brainstorming ideas for encounters with Pazuzu.
1) He’s a survivor. He survived the fall of the qlippoth race (or at least I think he did—I know he survived the fall of the obyriths in 3.5) to become a demon lord—no mean feat. He’s survived his worst enemy becoming a friggin’ goddess. And rather than sweat claiming one layer of the Abyss, he simply claims the skies. In all the layers. That’s insane…and yet he’s managed to hold on to them for eons and epochs. So if your PCs think they can just say his name three times, wait for him to appear, and ambush him, think again. Speaking of which…
2) He wants to be summoned. He makes it easy. Whereas other demons loathe being made to dance to a mortal’s tune, he appears like the Abyss’s concierge, prompt as you please. Of course, just saying his name three times means that he learns yours and opens you up to the threat of possession. And his wishes turn you chaotic evil with a crushing despair chaser. This is a demon lord who collects antipaladins as a hobby. What do you think your chances are of invoking him scot-free?
3) He will seem like the reasonable demon lord. Even more than the various succubus queens, Pazuzu will seem like the face of evil that you can at least work with short-term and remain unscathed. After all, he hates Lamashtu, right? Just avoid saying his name and making any dumb wishes and you can totally form some kind of alliance. The enemy of your enemy and all that.
Except he probably invented that saying.
Pazuzu is one of the worst demon lords there is. You just haven’t seen the full reach of his plans yet. If one of his servants does you a favor at first level, you won't see the other shoe drop until you hit level 20 and you snag some mythic ranks. But you will see it in the end. Guaranteed. And you will wish you hadn’t…except wishes are probably what got you into trouble in the first place.
I haven’t even mentioned Pazuzu’s mythic spell-like abilities, his aura of locusts and swarm mastery, or the poisonous snake he has between his—
You know what? Let’s get to the adventure seeds:
Trapped in the Abyss and cursed to be rejected by any Abyssal gate or portal, adventurers must get creative to find a way out. One option: Destroy one of the regenerating towers in Pazuzu’s realm, ride it skyward as it reforms, and slingshot themselves into the non-space between the Abyss and the prison moons of the Hag-Stitched. Of course, Pazuzu might take such a demolition personally…
Pazuzu may have been the son of a god whose corpse floats deep in the Astral Plane. Demons are not known for their filial affection, of course; in fact it is suspected that Pazuzu is the one who slew the entity known as Hanbi. But when a mysterious cabal of greater dorvaes put aside their differences long enough to begin mining the corpse (with the assistance of servants of the Old Ones), one of their shafts pierces the god-corpse’s lung…and Pazuzu’s name whispers across the multiverse. Now three powers want the corpse—particularly its heart, which Pazuzu wants to eat—and none can be allowed to claim it.
One of the souls Pazuzu has collected is the father of the tengu race. As the progenitor of an entire species, this soul has been protected from on high for eons and eons…but Pazuzu is nothing if not patient. Now, after millennia of vile torments, the soul of the tengu allfather coughs out Pazuzu’s name once…twice…and a third time…asking for surcease from his suffering. As the demon lord’s profane wishcraft takes hold, every tengu in existence begins to slide to chaos and evil. A party of adventurers must reverse the cursed wish and save the allfather’s soul, even as one of their own fights off the cold hand clutching the heart in his feathered breast.
—Pathfinder Bestiary 4 50–51
Obviously, the definitive non-Pathfinder take on Pazuzu is from Dragon #329, courtesy of James Jacobs. And since Mr. Jacobs is also one of the architects of Golarion, you can pretty much take that article as canon where it doesn't conflict with published Pathfinder material.