Hellhounds appear as gaunt, vicious-looking black canines that vaguely resembled Doberman Pinschers, but are much larger than any mundane dog. Hellhounds have shimmering red eyes, coarse black fur, a murderous temperament, and intelligence similar to that of mundane dogs'. They are used by demons for tracking and hunting, much like dogs. Hellhounds' jaws are its most dangerous weapons, their mouth as wide as sharks', their howls and growls loud and strong. Their tails end in a set of spiked nail-like protrusions, similar to a mace.
Lilith is able to command Hellhounds, as shown when she summoned two Hellhounds, in the form of shadows before solidifying, during a confrontation with Clary, Jace, and Simon. One immediately sprang for Jace, and the other was commanded by Lilith to pin Clary down.
Clary, before being crushed under the weight of the Hellhound, took her necklace chain and whipped it against the Hellhound's face, slashing the hound brutally across the eyes. The hound reared back, howling in pain, allowing Clary to escape. Bloody-eyed, the dog leaped for Clary but was beheaded by Jace with his seraph blade. It gave a single howl and vanished, leaving behind a scorched black mark on the stone, and the stench of demon in the air.