Duergahydra

Duergahydras, also known as the gray evil of the Underdark, were an extinct species of hydra that were notably quite smaller than other subspecies of hydra and inhabited the Underdark.

Description
These creatures had a hard, gray stony hide on what some would describe as a whip-like build. They had a central body the size of a tall human, two long necks each sporting a head, and a long tail. They typically kept one of their two heads bent around their body, laying hidden on their back to resemble a hump or folded wing.

Behavior
These creatures were quite aggressive and bold in their hunting, frequently sticking their necks out into danger, owing to instinctively being aware of their regenerative ability. They were also quite cunning, quickly learning the details and tactics of any foe they faced.

Abilities
Duergahydras were swift and agile climbers, capable of clinging to walls, and could see in areas of complete darkness. Like any hydra, they had a regenerative ability that would grow two necks and heads whenever one was severed. However, due to their size, they became slower with each head and neck they gained until they were reduced to a crawling movement and eventually became to slow to hunt and thus starved.

Ecology
Duergahydras were a rather solitary species, only pairing up when it was necessary to mate.

Diet
These creatures were an omnivorous species.

Usages
The blood of these creatures was quite useful for the creation of healing potions and regenerative potions.

History
The useful applications of the duergahydras' blood was discovered by drow and mindflayers, who hunted the creatures into near-extinction in an effort to harvest their ichor. Later on, humans became aware of their existence and attempted to train them as guardians or mounts. When this and efforts to keep duergahydras away from human settlements both proved impossible, humans began to slaughter the creatures whenever they saw one. Eventually, duergahydras went extinct on Toril around the year 50 DR.