The Plague Dog - is the final the product of a struggling human soul (a vessel) merged with that of a Purgatory Hound, forming what's known as a
mutt. A plague dog is still human, however, but with the added benefit of two souls and a twisted change whenever someone dies nearby. This type of Purgatory Hound requires all the necessary requirements a human needs to survive, and in fact the human still remains quite human. It is only when the dead lingers near, or someone passes that the Purgatory Hound inside of them is trigged, taking on a large physical form and seeking to fulfill the same duties as had been previously instructed.
Plague dogs are considered rogue Purgatory Hounds, since they cannot by controlled directly be Purgatory. They are
independent, despite being ruled by instinct. However, due to their
strong instincts they are permitted existence so long as they contribute their purpose to the benefit of Purgatory. Often they will form packs to rule and maintain under their command in order to fulfill this tameless desire to ferry the dead back to Purgatory (which they can venture). Like how birds migrating south for winter, a Plague Dog simply knows what to do and how to act.
