Advantage/disadvantage pack amounts to +15 points in balance. Under the standard GURPS rules, Horned Ones would have a racial cost of +45 points, but I've always used the "they cost what they cost" variation of racial- average stats; if you want to use racial stat bonuses instead, help yourself.
The moniker "Horned Ones" derives, obviously, from the pair of serviceable but blunt horns that all post-adolescent males (which are the individuals most frequently encountered by outsiders) of the species feature. Their own various names for their species are not translatable, since their languages are entirely composed of signs and postures, having grown out of natural body language; Horned Ones are totally mute, although they have quite good hearing.
Nevertheless, here follow a few notes on the "natural" Horned One society; the state of the art at native TL 0, so to speak. Horned Ones live in large extended-family groups; they are very territorial and prefer to live in areas of forest or mixed-vegetation terrain; they prefer to permanently inhabit either natural or artificial dwellings that are easily defended against predators and the like (inevitably, most available natural caves are inhabited; they also build houses out of wood, stones, clay, or whatever they have at hand). A typical Horned One community lives in one large interconnected building or cave complex with multiple entrances; they tend to agoraphobia (but far from universally) more often than to claustrophobia (which is practically unknown). A larger region inhabited by many Horned One communities would be divided into blotch-shaped territories (theoretically circular, but squeezed together here and there by difficult terrain, rivers, and other territories), each with a dwelling complex near the center.
The child-bearing females are the heart of the community, and if anyone can be said to be the bosses, it's the mothers and the grandmothers -- and when a community has an undisputed leader, that leader is the most respected of the older females, often known as Great Grandmother. Horned Ones have two sexes, and give live birth; pregnancy takes nearly a year and is somewhat more immobilizing (particularly toward the end) than for humans, although it's not nearly as risky for the mother. Single births are the norm; Horned Ones invest great amounts of care in their children, although they are born more well-developed than humans (being able to crawl and even walk -- although unsteadily -- within hours of birth). Children are reared communaly by all the females, although each individual child receives extra attention from its birth-mother. Giving birth to many healthy children increases your status among the other females, and is usually a prerequisite for becoming Great Grandmother. Most crafts are the domain of the females; they have plenty of time to pursue such things.
Reproductive maturity is reached around the age of 8 or 9; most communities practice expulsion of males as soon as they reach this age, so as to prevent inbreeding -- the adult males of any Horned One community are usually imported from other communities (sometimes by haphazard assimilation of desperate wanderers, more frequently by arrangement with neighboring communities). Females, on the other hand, can often live out their entire lives without ever going beyond sight of home (or even without venturing out of doors, in some cases). Every Horned One community is a panmixia; males are selected as desirable (or rejected as undesirable) by the community as a whole -- any applicant must first announce himself at the border, meet a patrol of males who may choose to reject him or to escort him in to the center, and then pass muster among the females.
While the females mostly stay at home, the males have to keep the community fed; their job consists of patrolling the communal lands (in medium-sized groups) to gather food and chase off any potentially dangerous predators (or infringing neighbors). The size of a community's lands is usually dictated by how far from home the patrols can effectively range; the total population of a community is dictated by how many Horned Ones can be fed off the food available in that area. Primitive Horned Ones seldom range more than half a day's leisurely walk from the center; spending the night outdoors (where it gets cold, and nasty things might try to eat you) is not fun; depending on the fertility of the local ecosystem, a community's population is usually a few hundred. Males usually go armed to defend themselves against predators; they have no interest in hunting for food (being pure herbivores), but it is not unheard of for them to undertake organized hunts in order to wipe out predators. They practically never use missile weapons (due to their lack of depth perception), preferring to carry stout wooden spears (probably flint-tipped) and various defensive implements (shields, etc). They also make frequent use of different noisemakers for signalling purposes (since they can't shout or scream).
Horned Ones' relationships with their neighbors can be extremely variable. It is not uncommon for one community to fight prolonged wars with another; they are capable of holding grudges for generations, and such a war can even end in the destruction of one community -- where the central dwelling complex is stormed and all the children and females slain (despite the fierce and dedicated resistance the females will put up). Abduction of children or females is practically unknown, since it would be fairly pointless -- any group of males large enough to storm a dwelling complex will belong to a big community with lots of *friendly* females and children, and besides, Horned One psychology classifies enemy females as the *heart* of the enemy -- if you took living females away from the enemy's stronghold, you wouldn't be damaging the enemy, you would be transplanting a part of the enemy into the hearth of your *own* community, something that would inevitably lead to discord and tragedy in your own home. Rape is similarly not practiced; Horned Ones never combine sexuality and violence at all. Much more common, though, are limited clashes over border rights or tribute payments; such clashes are often ritualized into non-fatal contests which over time develop into regular border moots (often linked with the peaceful exchange of young males). One community may win dominance over another by various means, even to such a degree that it would not be incorrect to speak of empire-building. Interestingly enough, though, inter-community affairs are somewhat hampered by the fact that the females of one community (who call most of the shots internally) practically never meet anyone from the neighboring communities, so all interaction happens through males meeting near the borders. No Horned One community will gladly allow individuals from another community to penetrate very deep into its territory (unless the alternative is getting wiped out by much more powerful neighbors).
The first major revolution in Horned One society comes with the taming of fire. This allows them to colonize huge parts of the world that were previously off-limits (they are, after all, cold-blooded); it also makes long-distance travel by groups of males more tractable (overnight patrols aren't so bad if you have a fire for light and warmth). Therefore, it tends to lead to a rapid expansion and global population explosion, although the population *density* won't increase -- it's the total populated area that grows. It is usually at some point after the taming of fire that a community has to begin interacting not only with its immediate neighbors, but also with the next community over and the one beyond that one, since travel becomes more frequent. Often, this period sees the development of some kind of regional "highway code" where narrow bands around the borders of each territory are considered no-man's-land so that anyone may travel along them unchallenged.
The second major change (toward the equivalent of the Neolithic era) would be the development of agriculture. Obviously, this would allow much higher population densities, and the size of a community might soar into the thousands. Individual Horned Ones might become hard-pressed to deal with this increase in "family size"; they naturally divide the world into us and them (where "us" is everyone in one's own community, and "them" is everyone else), what happens when "us" become so numerous that you can't keep track of everyone any longer? (This calls for some more thought.... at this point, radically different Horned One societies might begin to develop.)