Lycanthropy in Innistrad
Lycanthropy in Innistrad is, truly, lycanthropy. Unlike other fantasy worlds, all lycanthropes take the form from which the term comes, that of the wolf. Or rather, a wolf-like form. There are no werebears or wererats like on other planes.
Also, lycanthropy is not contagious in the traditional sense. The common people of Innistrad do not know how lycanthropes propagate, but all manner of fears have cozily moved into the vacant space of knowledge. In truth, lycanthropy is a condition of a split soul caused by ritualistic behaviour. A pack of werewolves call to a would-be victim in the night with their howls, and the werewolf-to-be is drawn into the woods, where a nature spirit enters them, wars with their human soul, and the human and werewolves hunt together. Through the hunt, the nature spirit takes control, and the human slowly takes on wolf-like traits. When the pack has brought down prey, and the human tastes fresh, raw meat, the change takes hold, and they are forever more a werewolf from that point.
There is no known cure, and the most promising attempt to find one ended in a more powerful werewolf and a ruined laboratory.
The transformation into canid form is akin to the rage of a barbarian, the werewolf cannot stop their transformation or change back, it is frequently brought about by emotional or physical stress, and they lose all control of themselves. There is a ritual, however, whereby a werewolf who accepts their new dual nature can entwine their spirits and gain control over both their transformation and their actions in canid form.
In effect, this ritual is a magical item that cannot be given up. The ritual costs either 8000 gp, or 3000 xp, in effect being a Medium item, and takes up a magic item slot.
The Effects of Lycanthropy
The primary effect of Lycanthropy is the increase in mass. Even the shortest human will grow in size to at least 8 feet tall, becoming large size. Their strength and constitution increase by 4, and they gain a +4 bonus to Natural armor.
In addition, their skin thickens, granting them DR 3+character level, overcome by blessed silver, they gain the scent special ability, and their teeth and nails grow in size sufficiently to become formidable weapons (a bite and 2 claws, damage appropriate to their large size) which overcome DR as if magic or blessed silver.
Finally, lycanthropes are always able to recognize another werewolf in human form.
Generally, a werewolf will transform in response to emotional stress, physical pain, or moon light. A sufficiently experienced werewolf may resist change caused by the first two, but the moon cannot be fought.
Holy magic, in the form of special rituals and objects can prevent the change, giving even inexperienced humans the chance to fight it, but cannot prevent a change brought about by moonlight.