Hydra

The hydra is a reptilian horror with a crocodilian body and multiple heads on long, serpentine necks. Although its heads can be severed, the hydra magically regrows them in short order. A typical specimen has five heads. 
Supposedly the Hydra has its origin in the blood of the fallen Dragon god Learnacea, a rival of the goddess Tiamat.

Behavior

A rapacious and gluttonous monster, a Hydra snatches and tears apart its prey in a frenzy of feeding. When a Hydra has cleared a territory of food and driven off any creatures smart enough to avoid it, it moves on to seek its meals elsewhere. A Hydra's hunger is so great that if it can't feed, it might turn against itself, its heads attacking each other as the creature eats itself alive.

Habitat

Hydras are natural swimmers, dwelling in rivers, along lakeshores, in ocean shallows, and in wetland bogs. A Hydra rarely requires shelter from the elements, so it doesn't normally have a lair. Only in colder climes are Hydras drawn to the protection of sheltered caverns and ruins.