The island of Myrna is the center of magical studies and magic in Cresia. Sorcerers from Myrna are without comparison in skill and in variety of magical disciplines. The reasons for this is that the island itself is a center area of magical power in Cresia. The southern areas of Caheb are similarly affected by residual magical power, but in Caheb the manifestations of this power are different, volatile, seasonally amplified and with an apparently evil streak.
The Rat Shapechangers of Caheb are just one manifestation of the powers at work. They are solely found in remote areas of southern Caheb where the mountains lower to the sea. The initial shapechanging process is unknown and mostly affects only inhabitants of smaller villages who have spent their entire lives there. In some areas fishing and farming communities may suffer even a 10% population loss due to their people turning into shapechangers. Some of the shapechangers live among their families, but most become too violent and irrational to be tolerated as part of their former community. They are rarely killed and usually just banished from their homes to live a life of solitary vagrancy. Some form packs of shapechangers that loot and pillage.