Wolfos are a species of wolf-like creatures native to at least the lands of Hyrule and Termina. Typically living in the forests and occasionally moving out onto the open plains, they are a pack hunter, using their numbers to surround their prey from all sides and their intelligence to outsmart and outmaneuver it.
Two main species are known to exist. The first one moves around on all fours, yet can stand upon its back legs in order to strike out at its prey with its front paws. During winter their brown fur takes on a white color, aiding them in blending in with their surroundings. The second species is much more wolf-like, and lives in icy environments. They are capable of moving through the snow like a fish, and pounce on whatever prey they encounter.
While live Wolfos have yet to be encountered in the fanfic, the barbarians in the first chapter are known to wear their pelts while going into battle, most likely believing that the it would grant them the ferocity of a Wolfos. Also, the Hylian Deer was apparently wary of one, believing the the crackle of dry leaves being stepped on was the sound of a Wolfos stalking it.
Later on, a female Wolfos watching over its packs pups notices Link as he makes his way through the forest.