"A creature of brimstone and the souls of the damned. It’s not quite a Demon dog like Meg or Alistair, and far from possessing any sanity. They’ve been described as being the result of a dog damned to hell and spawned from eons of it’s own suffering."
Okay so the way that I feel the Hellhounds should work in this AU is basically when the dogs go to hell after centuries and centuries of being there, over a long period of time they start to become either Demon dogs or Hellhounds. A Hellhound is on a lower tier than a Demon dog, acting only on it’s untamed rage-full instincts. No hunter really knows which dogs become Hellhounds and which become Demon dogs, it’s guessed at perhaps being the character of the dog but it could very well be how long they’ve been in hell or how they handle it. The more cunningly evil dogs are believed to become Demon dogs, proof of that being Crowley and Meg.
The Hellhounds work under the rule of the Demon dogs, collecting the souls of the damned that sold their souls at a crossroads. Crowley of course has one, and they are also invisible in this AU. except for certain occasions~