Demon was largely grumpy throughout the film, and had somewhat of a rivalry toward Ted Brooks. Indeed, he usually manages to find some way to humiliate Brooks even if he can't bite or attack him directly: One notable instance was when Demon attempted to attack Brooks, only for him to climb up a tree where Demon can't reach him, resulting in Demon deciding to instead mark the tree Brooks was on as a way of hinting that he now owns the tree. However, it was later revealed that most of his bad mannerisms stemmed from a bad toothache, which eventually led Brooks, when trying to search for his father, James "Thunder Jack" Johnson, when he went missing during the Arctic Challenge, to literally bite Demon in the ear, shocking even Johnson as he "didn't expect anyone to be stupid enough to try it." Afterward, Demon reverted to his good traits when the bad tooth was removed. Demon eventually repaid the favor when his team nearly went over a cliff by dragging the sled back up single handedly along with his team.
Afterward, he attended, along with the rest of the dogs, at Ted and Barb's Alaskan wedding and later, had four puppies with Nana.
A foreshadowing of Demon's toothache is when he is rummaging through Ted's bag and comes across his toothpaste. Demon steps on the tube, squirting some contents onto the floor, then licks them off.
Talking Demon in Ted's crazy dream
Talking Demon and the other talking dogs at the beach in Ted's crazy dream
Demon and the dogs at Ted and Barb's Alaskan wedding