Were-creatures, typically wolves though sometimes other animals do happen, do exist, however they are extremely rare, as they would have to have been cursed by the gods themselves. If anyone wants a list of gods and what they represent they can owl me. They essentially, like Straids, live forever barring illness or death by unnatural means. The time that they are cursed to be transformed varies, depending on the crime that got the gods attention(It needs to be really extreme to get them to personally get involved). The most extreme case is one who was set to be permanently transformed, as well as being trapped in a magical prison. The average is about a week per month with the central day being on the full moon.