The Dog Skeletons are 3 dead dogs that turned into skeletons after licking the God Bone for a long time, unlike Duncan. In Stormy Weather, Charlie the Mouse told Courage that Duncan was in the sewers. As Courage finds a huge bone in the sewers, he finds Duncan licking it. Courage tries to get Duncan to stop licking it, but Courage himself couldn't resist the taste of bones. Courage stopped his tongue and carried Duncan with the giant bone.
3 Skeleton Dogs came to life and they cornered Courage, except Duncan. They hit Courage with their bone clubs however Courage uses the giant bone to crush the Skeleton Dogs.