As the name implies they are the hounds commonly found in fiery dungeons. They have a Hit point based fireball. At full strength they do around 15 points of damage. Individually they are not too much of a problem, but unfortunately they are never alone. Hell Hounds spawn in groups of 5-8 and attack as a single group. Attacking one of the Hounds will make the entire pack attack you. In this sense they can be very dangerous, as a group of fighters can quickly be overwhelmed as each warrior is taken down individually.
The Hell Hound Leader is a stronger version of the normal Hell Hound, and can usually be found in the company of a pack of the normal kind. It requires a bit more taming to tame them and they will take up 2 control slots.