Wow. . .impressive. I can't think of enough dark adjectives to describe the effect of your dark Fenrir, but I think one of the scariest aspects of this story is how real it seems. If there were evil werewolves, they would be just like this.
You use animal terms ("pups," "bitches") in an effectively unremarked way that emphasizes FG as non-human. The lack of affect in his thoughts also makes him disturbingly alien, yet lines like this one -- The magic of wizards was nothing to this help us understand (somewhat) how he feels, why he exults in his situation.
It's interesting to compare the similarities in structure, style, and concept between this story and the previous Fenrir fic in the fest: it's almost as if he has to be written with understatement and narrative fragmentation. Otherwise we'd hardly be able to fathom him at all. Yet what's probably most frightening in both stories is that we can still see human nature in him.