Cerbus

Saving Throws: CON +3
Rarity: Rare
Diet: Meat
Taming Difficulty: Hard
Starting Bond Points: 2
Suggested Personality: Lazy, Aggressive

The deepest vaults of the underworld are watched over by fearsome, three-headed hounds. In places of lesser importance, where three heads would be overkill, a two-headed cerbus is an excellent guardian.
Twice the Dog. With its two heads, a cerbus is indeed more vigilant than a typical guard dog. It is not fully twice as vigilant, however. It is a question of the cerbus’ priorities: a cerbus’ two heads do eat twice as much as a normal dog, sleep twice as much, bark twice as much, and expect twice as many pets for being a good boy.
Burning Maws. When an intruder steps too far into the cerbus’ territory, the cerbus’ heart burns with indignation, and gouts of infernal flame fill its mouth like a furnace. Its barking sends sparks flying and its teeth glow like molten ingots, setting anything that it bites ablaze.
Snake-Headed Tail. A cerbus wagging its tail must be approached with caution, as a cerbus’ tail is in fact a venomous snake. As with most dogs, the tail is not under the cerbus’ conscious control. With twice as many heads to notice it, the cerbus spends considerable time chasing its tail; fortunately, it is immune to its own venom. Some may observe that the cerbus’ snake-tail has a head of its own, and argue that this means cerbuses are properly three-headed, rather than two-headed, dogs. Appropriately enough, large numbers of cerbuses prowl the circles of Hell to which fiends consign the souls of pedants.