It’s like my mother always said: “The enemy of my enemy is my spidery-limbed, whip-tentacled monstrosity born in an orgy of cannibalism.”
Wait. Your mother didn’t say that?
The good news is that thulgants hate demons way more than they hate you. And you may be beneath their notice, anyway—Ultimate Magic notes: “These powerful qlippoth are too arrogant and self-important to answer the call of a spellcaster wishing to bind them.” So if you encounter a thulgant in-game, your best bet is to quickly vacate the area or summon a demon and then run.
The bad news is that thulgants still want to snuff out every last vestige or mortal life and mortal sin. And they are born of the cannibalistic depredations of several augnagars, each of which likely left a trail of devastation in its wake. Plus, augnagars feed on rotted demon flesh, and as a general rule you really don’t want to be anywhere that is a) not only deadly enough to have demon corpses, but also b) so deadly that here are enough demon corpses to sustain an entire species. Oh, and thulgants are CR 18. And have ability score-draining stingers that can rip through your entire body, shredding every stat still further. But at least you can run from them—crap, no, they’re smarter than you (Int 24, Wis 27) and can plane shift as well.
So yeah, thulgants are bad news. Good luck.
Adventurers carefully pick their way through a qlippoth-infested layer of the Abyss, protected by charms that hide their mortal nature from the inhabitants. But the charms only work on fully mortal blood…as their pitborn (demon-blooded; see Blood of Fiends) tiefling discovers when a thulgant bursts forth from its trapdoor lair to devour her.
Adventurers help a renowned circle of wizards dismantle a cult of the Great Old Ones just days before a foul rite was to take place. But they are taken by surprise when the wizards attempt to actually finish the cultists’ dark ceremony. The wizards believe that by completing the summoning, they can entrap the entity for purposes of study and intelligence gathering. But it all goes wrong when the rite calls the wrong monster: not the expected star spawn, nightgaunt, or moon-beast, but an enraged thulgant instead.
A thulgant seeks to become a qlippoth lord, committing the twin heresies of individuality and worship seeking. It makes its way to the dying elven nation of Keshelar, where it teaches cultists that acts of cannibalism and murder will return vitality to their increasingly infertile race.
—Pathfinder Bestiary 2 226
What’s that? You have a long drive tonight/tomorrow for the holiday? Did you remember to download two hours of me?