Balverine

"The howls pierced the cold winds and before I knew it, they sprung from the shadows." - Walter Septua, The Amersellen Times.

In the first days of civilisation, when Isenwalt still belonged to gods and savages, there existed a creature known as the Balvorn. None know from whence it came, but humans were its prey. It would descend upon settlements to feed, devouring thousands at a time. Only one man ever survived a Balvorn attack - however, he was cursed by it, becoming a beast reminiscent of the Balvorn itself. He became the first balverine.
Balverines are lycanthropic monsters - bipedal and still recognisably humanoid, though grotesquely deformed and with a mixture of bat and wolf-like characteristics. The curse is spread through bites - one who is bitten by a balverine, but survives, may become a balverine themselves. They have long been a subject of campfire horror stories and cautionary tales for children
It is said that those Balverines who ascend to be an alpha of their packs become a white balverine. Rare and instantly recognisable by their distinctive colouring, white balverines are natural leaders - stronger and more intelligent than their normal counterparts, which bow to their will. Other variants of balverine also exist - 'bloodied balverines' distinguished by their blood-red fur, are stronger than regular balverines, and tend to take leadership roles within a pack in the absence of a white balverine. Frost balverines are native to Northern Isenwalt - their icy-blue colouring and increased hardiness are likely adaptations to the harsh conditions.
Worryingly, it seems that rumour gives way to their possibly being an artificially-created balverine, these tales naming it as the "poison balverine."
Balverines form packs, which hunt as a group - leaping on their victims and tearing flesh from bone with their terrible claws. They are vicious and incredibly agile - one would have to be either incredibly lucky or a supremely capable warrior, or perhaps a hero, to survive a Balverine attack.
Savage though they are, they are not all mindless beasts. The more cunning balverines can take on a human shape to disguise themselves, often luring unsuspecting travellers into traps as food for their fellow monsters. This behaviour has been increasingly noted in later ages - whether this indicates an evolution in balverine behaviour remains to be seen. There have even been some reports of secret societies of balverines, with goals of infiltrating positions of power within Isenwalt - though there has been little in the way of concrete evidence.
There is a long-standing myth that Balverines can only be killed with silver. Though they can in fact be killed by ordinary weapons, there is, as is often the case, a grain of truth to the superstition - balverines are more vulnerable to silver than other metals, and some unusually-strong white balverines have been known to develop hides which could only be pierced with silver. In lieu of silver, fire and magic are said to be just as damaging to them.
If one is brave or foolhardy or simply unfortunate enough to spend an extended period in balverine territory, the need for long-term protection cannot be overstated. Readying and maintaining a heavy supply of magic and fire will severely weaken any balverines that approach, and ensure that they keep their distance.