I agree, there are some tough ones, and it may get tougher as we go!
As much of an awesome nasty the serpent was, we don't really know much about it. Its world-building was solely to be 'a danger on the path', and possibly to demonstrate how powerful Onni could be.
Our poor hound, on the other hand, had a whole implied backstory in the form of a collar with a little heart-shaped tag on it. That little detail, within the whole chapter that gave us so much detail in its worldbuilding (crap buildings, worms in the eyes, sunlight restoring a sense of self, immune animals, Emil & Sigrun & Mikkel's reactions to the mama cat, gramophones, and kallohonka...) Unparalleled.