Dustin, feeling like a bit of a fifth wheel now that Max is around, befriends a slug he finds in the trashcan, which . . . dude. After the events of season one, you should totally know better than that.
Lo and behold, the slug turns out to be a baby demodog and ends up eating Dustin's cat (RIP, Mews). Eventually, Dart has to die like the rest of the evil, man-eating dog-things . . . but not before Dustin gets to say goodbye with some nougat.