"The creature resembles a big, powerfully built dog with short, rust-red fur; its markings, teeth, and tongue are sooty black. It has red, glowing eyes."
The hell hound is an outsider from the Nine Hells of Baator. It resembles a mangy, skinny, somewhat demonic hyena-like creature with red eyes and draconic ears. It has the ability to breathe fire.
Hell hounds are efficient hunters. A favorite pack tactic is to surround prey quietly, then attack with one or two hounds, driving it toward the rest with their fiery breath. If the prey doesn’t run, the pack closes in. Hell hounds track fleeing prey relentlessly.
A larger version is the Nessian War Hound, a coalblack mastiff the size of a draft horse, often fitted with shirts of infernal chainmail.