Hell Hounds are Lawful Evil creatures from another plane. They will attack on sight.
Being Lawful Evil they are vulnerable to Holy and Anarchic weapons, as well as the appropriate Bane sub-type.
Hell Hounds are very sneaky prefering ambush over a straight fight. They will use their superior Hide and Move Silently skills to sneak up on Adventurers.
They also possess the innate ability to breath fire in a small arc causing damage to any in front of them.