Allow me to quote the Bestiary 4:
Like some taut pustule ready to burst, this mobile wound scuttles on a bristle of slick hairs.
It’s an animate diseased boil that attacks you! And upon dying, the boilborn explodes in an acid burst! If you’re reading this, roll up a character, because I want to attack with one of these right now.
A recent trip to the Furnace left the imp Xytaxis infected with infernal boilborn. His infestation already killed his master, which may or may not have been a violation of his contract with the sorcerer. Fearing demotion, Xytaxis is in hiding until he can research the matter; meanwhile he calves more boilborn on a regular basis.
Some risk-taking apprentices have broken into a disused wing of the Halls of the Magi. The ringleader is after a stash of pickled carbuncles. (Rumor has it that these make excellent spell components…or narcotics.) What they find is the reason the wing is disused—a fountain of sewage that defies magical dispelling—and that whatever specimen bottles are still present are all infested with boilborn.
Death in battle is the only honorable end for a hobgoblin. Those who make it to old age continue to serve the war effort. After a sack, hobgoblins will often leave a diseased elder to lie among the wounded to leap up and attack those who come to offer healing or bury the dead. Hobgoblins are prone to blinding sickness, and blindborn sometimes birth themselves from the elders before they even have a chance to take their final revenge.
—Pathfinder Bestiary 4 22
Like so many grad students with too much time on their hands, I sent in a submission to the contest that would one day yield Eberron. Plague was a big feature of mine, so I think boilborn are cool, period.
Pro tip: If your campaign take place in the Mwangi Expanse, Southwest flight confirmation numbers make great Bekyar names. One day I will unleash Mokube the Eater upon the world!
Speaking of which, unexpected travel plans may interrupt posting over the next two days or so. Bear with me!