There are plenty of options for what to do with werewolves in Fianyarr. In fairytales, werewolves represent the repressed brutality and cruelty within us all that can be sparked by rage and insanity into a terrible moment of violence that leaves us devastated and confused. Within it lies the seed of every real life story of a mother who kills her baby because it wouldn't stop crying or spouse who kills the beloved they found in bed with another person. They also represent our fears toward those people within the community that hide terrible acts behind a calm facade, sneaking off at night to butcher their victims or abuse their family members. Thus the werewolf is a seemingly normal person who flies into a primal rage when the moon is full, transforming into a monster that stalks the lands, before reverting to their human forms.
In a darker story, the werewolf is a normal person outside of those moonlit nights and those who confront them are forced to kill an otherwise innocent person driven to madness by a curse. The somewhat better option is the werewolf curse that strikes an innocent and makes them evil so that they are sociopaths during the rest of their days which at least allows the PCs a chance to kill them without wrestling with their conscience. In less dark tales, the werewolf was an evil person cursed to reveal their evil on nights of the full moon.
In more modern tales, werewolves are more ambiguous creatures who are neither inherently good nor evil. Perhaps this is due to our fascination with anthromorphising animals (thinking of animals as people) or perhaps it's simply the result of so many childhood years wishing we could grow fur and fangs so that we could run with the animals. Sometimes the werewolves are more in touch with nature. Sometimes they still have that bestial rage but it is tempered by human reasoning and compassion. Sometimes the werewolves actually are more, y'know, wolfy and have a more animalistic nature that encompasses a wider range of wolf-like behaviours. After all, most modern werewolves behave more like Tasmanian devils with their aggression and viciousness rather than the more socially inclined wolves.
But all of that aside, how would you like your werewolves?
Firstly, think of the transmission. Are they born or bitten? Both work in a light fantasy or dark horror setting. Those who are born to be werewolves might grow up as humans before transforming into monsters on some heart-rending night that involves the loss of their sweethearts.
Secondly, think of whether you want them to be the ambiguous evil (lots of heavy hearts and emotion surrounding their deaths) where they are never common and each instance is a moment of tragedy. Or whether you want a chance for your PCs to cut down an entire pack of evil nonhumans without having to worry about feeling sorry for them the way a PC might feel sorry for cutting down an evil mercenary warband. Or whether you want them to be another race in their own right, complete with their own traditions, mannerisms, hopes and dreams. Or outsiders who hide away their strangeness for others. Or something in between.
You could even have two superficially similar werewolf strains but where one turns humans into shapeshifters, the other makes them rampaging monsters. That would certainly make sense for an alchemical poison transmitted through the saliva. Perhaps the failed variant turns folk into killers and got loose from the alchemical laboratory. Who knows?
Finally, how will you create them? Naturally they need to be able to turn into wolves but that could be as simple as creating a Nixie and giving them the ability to turn into a wolf by spending a glamour. Alternatively you could use the Werewolf: the Forsaken wolves and pick whichever gifts and auspices seem to work. You could even use the disciplines from Vampire: the Requiem but make it so that the werewolves have to eat human meat rather then drink blood to regain their 'vitae'. The physical discplines such as celerity, vigor and resilience, not to mention Nightmare and some of the bloodline disciplines are all quite fitting for a home brew werewolf.
With all that in mind, you should be able to develop your own werewolves pretty easily.
So what would I typically do with werewolves?
I like giving them a little complexity so I would be most prone to developing them into little communities of about 30 who oversee their territory. They clash with the agrarian settlements that are start to push forward and through their territories, especially as the settled races don't recognise the werewolves' sovereignty and so expect to buy and sell land through other people. If the werewolves build their own homes or start to sell their own materials, they would be liable for taxation by the nobility. The fact that werewolves are also far superior in combat abilities compared to the average person means that the nobility are also eager to have the werewolves swear themselves into vassaldom so that they could be fielded in battle against other liege lords.
This naturally is creating quite a bit of tension and the situation has reached a political stalemate. Unfortunately for the settlements the werewolves are supreme guerillas with greater power, regeneration, and raw desire to win then the average conscript. Unfortunately for the werewolves, the settlements have a huge numerical advantage and even if the settlements were entirely wiped out there would soon be more as people from neighbouring countries seek fame, fortune and freedom in their lands - quickly repopulating the lost settlements.
You can imagine that a campaign could easily form from this along as the PCs try to navigate the political complexities of the situation, choose sides, and try to find a way that is palatable to all.
Of course, in reality, you'd need a third party to foster unification before anything got done. Perhaps a sociopathic necromancer hell bent on world domination? Or a sentient plague trying to destroy everyone in those lands? I wouldn't introduce the third party until well into the second Act. Best let the players muddle about in their sandbox first.