Hell hounds were fiery beasts found around the Lower Realms. They resembled monstrous Dogs with powerful physiques, standing between 2‒4.5 ft (0.61‒1.4 m) high at the shoulder and weighing about 120 lb (54 kg). Their fearsome forms were covered in short, rust-red or red-brown fur and their eyes glowed red. The markings on their bodies as well and their fangs and tongues were the color of soot, and they reeked of sulfurous smoke.
Hell hounds, being intelligent beasts, could be trained and commanded by various entities across the planes, but their inherent malice limited their versatility. Outside of retrieving specific objects, most could only be trained to kill, often abandoning or betraying masters that forbade them from sating their merciless hunger. Even if not specifically trained, they stole items from their deceased victims to use as playthings, such as noisy bags or pouches containing a victim's treasures, toying with them until the flammable components eventually turned to ash and the remains littered their dens.
Hell hounds were very stealthy creatures, and unlike ordinary dogs they did not howl when hunting, instead quietly stalking their prey and surrounding them in a ring. One or two hounds would immediately use their scorching fire breath to drive their quarry into the waiting, fiery fangs of the other pack members, unafraid of harming their other infernal companions. The dietary needs of hell hounds were similar to those of ordinary canines and they would consume anything that appeared edible. The flesh they consumed fed the fires within them and they only occasionally brought food back to their dens for later consumption, preferring to eat at the site of the hunt.
In the wild realms of the Lower planes, hell hound packs could be as small as a pair or contain up to twenty of the vicious beasts. The largest and strongest hell hound became leader and drove off any competitors, forcing them to establish their own packs and territories. Territories were somewhere between 5-14 miles centered on their dens and could overlap with one another.