Rats actually did manage to survive the freezing of the city in some of the ancient sewer systems. There they scavenged any food they could find, including potions and other magical items. Somehow, over the centuries, at least one strand of rat grew to the size of cats. Usually, giant rats are encountered in small packs.
Bad tempered and aggressive, wild boars are also very tasty and thus much sought after in the frozen north.
Metal miniatures, supplied unpainted.