Hydras are especially deadly monsters, since whenever a head is severed, two new ones grow in its place. They are not very intelligent. They typically live alone in swamps and are generally always the most dangerous predator in whatever area they inhabit. A hydra is gray-brown to dark brown, with a light yellow or tan underbelly. The eyes are amber and the teeth are yellow-white. It is about 20 feet long and weighs about 4,000 pounds.