Their appearance is as shrouded in mystery as their origins. They are never seen without their cloaks, masks, and gloves, as these are the chief identifiers of their station. The masks are akin to those of crooked-beaked birds, cast in silver, with strange carvings all over them. Their gloves appear to be the finest in dark calfskin leather, almost vanishingly thin, but never tearing, and upon their left index finger they wear a silver ring, shaped like a bird's talon, and just as sharp. Over their mask, they wear an oilskin cowl, and over their cowl, they wear a heavy oilskin cloak. IF any member of the Arrostekomistes would be seen outside of their uniform, they would not be recognizable; therefore, no member of the Arrostekomistes has ever been seen, only the uniform they wear.
The Arrostekomistes seem to abide by a philosophy of "a little harm now prevents a later calamity." They do not seem to have any ability at all to heal diseases once they have attacked, and have no interest in being around the diseased. Therefore it is unclear whether they themselves have already been inoculated against all of the diseases in their bandoliers, or whether they do their job, and move along as fast as possible in order to avoid infection, utilizing their masks and gloves as ways to further protect themselves.
The method itself is straightforward: The plague-bearer picks a vial from his wide bandolier, the disease to be inoculated against, and very deftly and carefully pries the silver lid open just enough to fit the tip of his ring down into it, to rub against the small lump of something that is inside. Then, he grabs the patient's arm, and scratches small five parallel lines into it, just barely enough to draw blood. The result looks much like a cat scratch, though the lines are unnaturally uniform. As soon as the scratch is complete, he stands up, and walks away. Arrostekomistes accept no payment, do not bargain, speak very little, and do not linger. They have also never been observed eating or sleeping, though they obviously have to do those eventually.
In their own lands, Arrostekomistes are treated as bogeymen among children: a visit from the Arrostekomistes is a fearful and potentially deadly thing, yet many parents still take the risk in order to prevent greater harm from coming to their children. Young children are never inoculated, only once they reach a certain age. It does not matter if they are human, elven, dwarven, or even dragonborn, orcs, or tieflings. Anything that can contract a disease, the Arrostekomistes can try to help. To have the scar from the inoculation has subsequently become a rite of passage among children in some places: it means you have survived the infection, and become stronger.
Inevitably there have been those who have harassed and manhandled members of the Arrostekomistes, but they do not usually live for long; usually coming down with all manner of strange diseases. It is as if the Arrostekomistes are able to create a deadly aura of pestilence around themselves when they are at risk, since none have ever been reported murdered or seriously injured, only the aggressors. Furthermore, those who would attack one of their order are shunned, and their families shunned, and their family's families shunned. Some doors they will pass by no matter what sort of payment is offered them. Nobody has known any of their order to lash out or to make someone sick who wasn't deserving, but the mystery and silence about them is so complete that one wonders whether one would ever know if they had.
[Spoilers] It is a secret fact that many of the older Arrostekomistes are actually undead, continuing to perform their duties even beyond the grave. Members of their order go through many magical rites where they cut all ties to their families, their countries, and their identities, and become one of the order irrevocably and permanently. Many will still grow old, feeble, and infirm as normal people do, but some are changed in unexpected ways. Instead of growing older, they grow stranger: slowly the life disappears from them, yet they continue on their missions, traveling from land to land, administering their inoculations, sometimes for hundreds of years. When it is time to retire, they return to the secret base of the order, where they are magically put to rest.
They have in fact been rendered immune to most diseases and most poisons, and necrotic or weakening attacks do not affect them. Their oilskin uniforms are slightly resistant to fire (resist 5) but repeated attacks will eliminate that resistance. The magic that binds them to the order also gives them certain exceptional abilities, such as resistance to sleep (they don't ever sleep) and inability to be dazed, blinded, or stunned. Additionally, they give off an aura 1 Miasma of Pestillence, which will be outlined in a later stat block.
If one is actually killed, its body will begin to decay immediately, crumbling into powder and poisoning the ground around it. Anyone nearby will be very likely to contract a serious disease. If it manages to escape, other members of its order will avoid contact as much as possible, and towns where they are staying will not be visited by Arrostekomistes. Likewise, if one is killed and its accoutrements are taken, others will quickly find out about the crime and regard the party suspiciously. Those who mistrust and fear the Arrostekomistes, however, will be very interested in any information about them that can be shared.
Most Arrostekomistes are within low- to mid-Paragon level, but very old undead members can easily rise into low Epic level.