Symbolism, Imagery, Allegory
Lone Marten
Gwin is a marten (a critter kinda like a ferret) with horns. Though martens don't normally have horns, Gwin's from a fantasy-land, which his horns—since they don't exist on real world martens—remind us of. Gwin belongs to Dustfinger, and their close relationship actually points us toward what Gwin symbolizes in the story: Dustfinger's lack of belonging, along with his survival instincts.
Consider this: If you see a cute little furry mammal—let's say a squirrel—while walking down the street one afternoon, you probably wouldn't give it a second look. However, if this was a horned squirrel, you'd definitely give it a second look… if you weren't too busy running away, that is. One thing's for certain: you'd recognize something as off immediately. Your attention would inevitably be drawn to just how out of place this critter was. And though you've probably seen more squirrels than martens in your days, this premise is true when it comes to Gwin too.
It is also true of Dustfinger. It's not that there aren't wandering fire performers in our world, or guys who can juggle and put on a good street show—it's that Dustfinger, no matter where he goes, simply doesn't fit in. For instance, at one point he notices some women in a town staring curiously at him: "Dustfinger often attracted such glances; anyone could see he didn't belong here. A stranger forever" (26.19). In other words, just like Gwin, Dustfinger sticks out as strange and otherworldly.
Survival Skillz
After everything goes down with the Shadow, Dustfinger runs into Farid and asks how Gwin is doing; Farid reports that Gwin ran away during some gunfire, but then came back. Dustfinger replies:
Well, he always knew when it was time to run, just like his master. (58.18)
So we aren't the only ones who see a parallel between Gwin's survival-oriented behavior and Dustfinger's behavior. Dustfinger sees it too. And when he says, "A marten like Gwin will always survive" (58.20), we suspect that Dustfinger will always survive, too. Come to think of it, we never really think he'll die while reading, not even with all that Basta and Capricorn put him through. That's because Dustfinger knows how to look out for number one.
It makes sense that Gwin—a wild animal—symbolizes Dustfinger. After all, Dustfinger himself is pretty wild—he definitely doesn't fit in with civilized people—and has strong survival instincts. Plus martens are adorable—and Dustfinger's not quite as tough as he'd like everyone to think he is (check out his write-up in the "Characters" section for more on this).