Clearly someone (okay, it's wesschnieder) knows their obscure Catholicism. Ten bucks says there’s also a pun in there (the Latin “ostium” for door not being far from the Greek “osteo” for bone).
So ostiariuses are the kyton race’s gatekeepers. But more accurately, they are gate tenders—doormen to the multiverse’s creepiest BDSM club (risk and kink, yes; aware and consensual, definitely not), carnival whisperers rather than barkers, touts whose job it is to set the hook, dangle it, and see who (ceno)bites.
Ostiariuses also fulfill a utilitarian role in the metagame, as they are low-level monsters that usefully explain how kytons and other servants of Shadow are able to so easily move between the Material and Shadow Planes. But this has interesting implications at the story level as well. Ostiariuses who travel about might be the means sought by PCs questing for a plane shift at low levels. Ostiariuses who tend stable portals are likely to figure heavily in the lore as well, becoming landmarks unto themselves. In a low-magic campaign, an ostiarius might be one of the only outsiders a party ever meets—a dark, seductive figure hinting at whole other realities lying just out of reach…or worse yet, just within.
The war college of the Legion of Might has a particularly demanding and seductive professor of rhetoric: an ostiarius who came to seduce the third head of the Legion…and having succeeded, never left. His “salary” is whichever students fall under his sway—never more than three a semester—who are subsequently deemed washouts. Adventurers trying to infiltrate the war college will find him a sympathetic ear and an invaluable source of magical assistance…but the prices he charges for his services begin at a pound of flesh and grow ever steeper.
The ostiarius Moriel tends a Shadow gate in an unusual place: Heaven itself. Pallas is an archon-held garrison city near where the Second Heaven gives way to the lawful neutrality of Agria-Thrace. Moriel’s charge is a disk of roiling black energy under an arch in the shadow of the basilica there. The archons would exile or execute Moriel if they could, but as long as the faith of Rageth the Self-Flagellator is popular among Pallas’s angels, they may not move against him.
Invited to the Spring Fete as an ambassador from the Plane of Shadow, an ostiarius begins to twist the royal garden party to his ends. After subtly using his spell-like abilities to throw the festivities into confusion, he makes his way to the hedge maze to enthrall the princess and persuade her to plane shift away with him. Musketeer adventurers hoping to rescue her must navigate the maze and contend with startled guests, dangerous living topiaries, and the kyton’s fetchling, augur, and lampadarius footmen.
—Pathfinder Adventure Path #64 86–87 & Pathfinder Bestiary 4 176
The full entry in PAP #64: Beyond the Doomsday Door has an extended section exploring ostiarius rhetoric and skill at persuasion you’ll want to check it if you dig role-playing these outsiders.
On another note, Magic of Faerûn had a fey take on gatekeepers: a Huge fey known as the crossroads guardian.
I’m sure one of you is now going to tell me which Hellraiser franchise cenobite inspired the ostiarius. Since I’m never going to watch those movies ever, I’ll take your word for it.
I’m really psyched at how this radio show turned out (aside from the fact that the stream ripper kicked on a minute late). Songs for Father’s Day—including, yes, a certain Martha Wainwright song—Teen Men, new Indigo Girls, classic Belly, a dash of reggae, and more. Stream and download it here!
(Link good till Monday, 6/29, at midnight. If the feed skips, Save As an mp3 and enjoy in iTunes.)