The Unknown Shadows come from the world of Hsien. They are similar to the Shadows that infest the Plain of Glittering Stone, but are more intelligent. While the Black Company resides in Hsien, Tobo befriends the shadows and becomes a messiah of sorts to them. The Unknown Shadows leave with Tobo when the Company goes back to Taglios and become the Company's key scouting resource under Tobo's direction.
Unknown Shadows can be deadly, as was demonstrated when one shaped like a giant duck with enormous teeth swamped Mogaba's boat and killed his crew.
There are an enormous variety of Unknown Shadows with a large number of traits, from panthers, to dogs, to owls.