Marraenoloth
From Ardrana
The marraenoloths are a special type of yugoloth. The thin, gray, pale-eyed humanoids are easily identified by their skeletal faces, somber hooded robes, and eyes that glow red when they are angry. They are a cold species mercenary at heart, like all yugoloths.
They are telepathic and, in addition to speaking all languages, maintain mental contact with others of their race at all times.
These yugoloths are not great warriors, attacking only with their bony fangs. When angered, their eyes glow fiery red, and anyone confronted by this horrifying gaze is likely to run off screaming. The marraenoloth then summon hydroloths to fight for it.
Marraenoloths are unique among the yugoloths in that they have an established task: They are boatmen who pilot small skiffs on the black waters of the River Styx, in service to Charon. Unlike many other fiends, the marraenoloths can pass from plane to plane without arousing suspicion in the minds of others. They are ferrymen and ferrymen only. Other fiends would love to subvert the marraenoloths to spy on their Blood War enemies, but these creatures are only concerned with their passengers.
Marraenoloths have an innate understanding of the twists and bends of the River Styx's channels, so they never get lost (unless it's convenient to do so). These creatures also can pilot their crafts through the Astral Plane and to the Prime Material Plane. A marraenoloth without a vessel is lost and useless, so they are naturally reluctant to venture far from their crafts.
Marraenoloths carry passengers but never cargo, always demanding immediate payment for their services. Since all marraenoloths are aware of each other, all know of any person who cheats or harms anyone of their kind. They won't come to each other's aid (that would indicate concern for their fellows), but the identity, of the transgressor is noted, and future services from any of these yugoloths will require greater payments and incur a significant risk of treachery. The cheater can return to the good graces of the boatmen only by making a suitable sacrifice to all their kind.
These are among the most neutral of the evil yugoloths, existing to collect their fares and nothing else. They stay clear of the politics of the Blood War. Because their skills are valuable to tanar'ri and baatezu alike, the other fiends tolerate this neutrality.
Note: Marraenoloths originally appeared in this form in the Planescape AD&D campaign setting from TSR. Their use here is for the purposes of providing context for the campaign only.