The Deep Tribes
There are three known Deep Tribes: The Beasthunters, the Greenwalkers, and the Fishers. Long ago, there were more, but the growth of sapient population of Arden has squeezed some tribes into extinction, and others have evolved into settlements that can no longer be called Deep Tribes (though there are often recessive traits in those groups that can bring out the magical abilities more common in the Deep Tribes).
The Deep Tribes are not Fae, but humans long twisted by exposure to the "pooled" magic of the most ancient parts of Arden. In fact, Fae tend to be highly uncomfortable around the living places of the Deep Tribes. Deep Tribemembers tend to be a bit short and lithe, and often have upswept ears. On a less cosmetic level, they're a hardy people, surprisingly strong, and several magical abilities tend to run in their bloodlines. Primary among these is the power of Twilight, though most never manage to develop it to the point of Shadow travel, and most of the Deep Tribes are xenophobic enough that they wouldn't Shadow travel if they could. Other abilities sometimes include healing abilities and animal telepathy.
The Deep Tribes are largely mysterious to outsiders. They are often highly
xenophobic, suspicious of those they perceive as invaders of their territory,
and liable to act on slights hundreds of years old. But even when they are
at their most friendly, the Deep Tribes are enigmatic -- few have the capacity
to pierce the primitive, but ancient culture of the oldest dwellers of the forest.
The Beasthunters are the most numerous tribe, and the most "cosmopolitan." None the less, they're a stone age culture, albeit such an old one that they have a certain non-technical sophistication. Unlike the other two tribes, they'll occasionally allow outsiders into their society briefly. They greatly prize their hunting skills.
The Fishers dwell on the Black Moor, where the largest river in Arden widens into a disturbingly quiet swamp. The Fishers pole about the Moor on their shallow-draught craft, and rarely speak even to the Greenwalkers or the Beasthunters.
The Greenwalkers are the smallest tribe, and they range the most widely
through the forest. They tattoo complicated camouflage patterns on their
skins, and are said to be some of the most powerful users of Twilight.
Guardians of Ancient Magic
All three Tribes make it their business to guard some areas of Arden where its ancient magic is twisted, and tends to mutate creatures into monsters. While they're not always successful in containing such monsters, Arden owes more than most know to the Tribes.
These areas of magic are likely responsible for the differences between Deep Tribemembers
and the human stock from which they are descended. Their status as deep, dangerous parts
of the forest are also doubtless responsible for some of the rumors that pass through
Arden, few of which are complimentary to the Deep Tribes.
A Dying Race
All three of the Tribes (especially the Greenwalkers and the Fishers) are seriously inbred at this point, and fertility among both males and females is on the wane. If current trends continue, the tribes will probably become too small to support a society in a century or two.
As their fertility declined, the Tribes have gradually created customs which might seem a bit bacchanalian to less endangered peoples. Four times a year (the solstices and the equinoxes), they hold festivals which look suspiciously like a quick framework for orgies. Which is accurate enough -- but three quarters of the children of the Tribes are the results of these festivals, and without them, it seems certain that the Tribes would have vanished long ago.
The Deep Tribes are heavily inspired by Anne Logston's fine fantasy books Shadow, Shadow Dance, and Shadow Hunt, as well as TSR's D&D supplement, The Elves of Alfheim. The material was reinterpreted, melded, and modified by Michael Sullivan (Epoch).