Hell Hounds are rare creatures not of this plane–they were brought from Hell by other, more powerful beings to serve as guards and pets. They can be found in ruins and other desolate areas, protecting their domains. Usually hell hounds will be the guards for necromancers or other powerful beings but sometimes they can be found in ruins–left behind after their masters moved on or were killed.
They are rust to dark red in color, with black fangs and glowing red eyes. Smoke is commonly seen to emit from their nostrils.
Hell hounds are very intelligent and aggressive, and will guard their territory to the death. They will stalk any intruders, and attack at the most opportune time. If the hell hounds are by themselves, they will wait to see if the intruders will move on in order to not bring attention to themselves. If they are guarding their master, they will attack regardless of the size of the intruding party.
Not much is known about the ecology of hell hounds. They do not seem to require a lot of food to eat, which reinforces the belief that they are supernatural beings. The are always found in uninhabited areas, ruins or powerful wizards’ lairs.
In addition to attacking with their black fangs, hell hounds are able to emit a short bust of flame at will. They are also able to move with great stealth, surprising prey 50% of the time.
Hell hounds commonly have ST 10, DX 14, IQ 7 and MA 12. Hell hounds attack by raking with their claws for 1d-2 damage, and biting for 1d damage. The effect of their fiery breath is that of a Fire spell cast in a front hex, doing 1d+1 damage. Their hide stops 1 hit of damage.
Hell hounds are also huge–typically 1 meter tall at the shoulder and weighing 70-90 kg. They are 1 hex creatures.
This writeup is based on creatures first found in AD&D.