Paizo has featured a number of astrology/astronomy-related monsters and locations (blink dogs come to mind, as do several adventure locations in the Pathfinder Adventure Path series)—not quite to the point of overuse, but it’s definitely been a strong motif. That’s likely because the stars and planets matter in Golarion—the planets are real places you can visit, many sorcerous bloodlines and oracle mysteries are related to the heavens, and there are dark things living in the Void. Not counting Spelljammer (where the stars weren’t mysterious, just new “dungeons” to visit) the only other setting that’s been as concerned with celestial movements was Eberron, whose dragons were obsessed with the Prophecy and whose planets tracked the movements of the planes.
I bring this up, of course, because lunar nagas are star-obsessed. Naturally, they don’t have to be, if you don’t want them to be—the default spell list makes a good case for a race of spies or undead-hunters, too. But let’s roll with the star obsession, because that makes adventure planning easy. A subterranean naga obsessed with stars is going to need a lair that winds up and down her mountaintop—a perfect dungeon for exploring. A limbless naga fiddling with complicated telescopes is going to need a host of minions to help, lots of magical aid, or even PCs to run errands (or to try to steal from). Other awesome locations to find nagas: an orrery, a planetarium, a stone circle, a crop circle, the site of desert geoglyphs, a glacial observatory, a ruined wizard’s tower, a giant stone calendar or sundial, and so on.
So however you want to use lunar nagas—as friends, foes, foils, side treks, or even employers—they are your excuse to go big on the set design.
An abandoned dwarven monastery has been retooled as a human prison—the monks’ spare cells and communal quarters being ideal for convicts. Wanting access to the monastery’s calendar room, the lunar naga Ovenia decides a prison break would be the fastest way to clear the facility. In her eagerness, she chooses the night of the full moon, unaware that lycanthropy is sweeping through the convict population.
The elven navy of Weareth is known for its fine ships (some of which are alive or even sentient), its magical might, and its navigational superiority. It is not always known for winning battles, however—sometimes attacking ports seemingly at random, or breaking off from engagements for no reason. This is because the elves rarely fight just for political or economic reasons alone. The Wearethen navy relies on lunar nagas as navigators and sages, and they do as the stars (and the chaotic neutral nagas) dictate—playing some long game that is dictated as much by celestial portents as realpolitik.
On Thirdearth, lunar nagas don’t just get their name because of their shimmering scales. They are actually from the moon. A trip on a skyship reveals a nation of albino lizardfolk ruled by a ruling class of lunar nagas, who regularly communicate with their earthbound brethren. Their plots may not bode well for the nations of men…but they are also Thirdearth’s only defense against even worse things living under the moon’s surface, including spirit nagas, morlocks, and demodand-worshipping troglodytes.
—Pathfinder Bestiary 3 197