Sea Hydra
Hydrae are immense reptilian monsters with multiple heads. For each Hit Die the hydra has, it will have one head. The chart above lists the THAC0 value for hydrae, the number of heads and the damage that they inflict each time they bite.
Hydrae are gray-brown to dark brown, with light yellow or tan underbellies. Their eyes are amber and their teeth are yellow-white. Hydrae have between 5 and 12 heads (d8 +4).
Combat
Hydrae always have 8 points on each of their Hit Dice and all heads must be severed before the hydra dies. A hydra can bring up to four heads into action against a single foe, biting once with each of them.
Each time a hydra takes 8 points of damage, one of its heads is assumed to have been severed. When this happens, a natural reflex seals the neck arteries shut to prevent blood loss.
Hydrae attack according to the number of heads they have. Therefore, a 10-headed hydra continues to attack as a 10 HD monster even after several heads have been slain.
Attacks on the body have no effect unless a single attack inflicts damage equal to the hydra’s original hit points.
Habitat/Society
Hydrae are solitary creatures who prefer dismal surroundings. They gather only to mate.
Ecology
Despite the hydra’s size and multiple attacks, they are often preyed upon by dragons. They are impossible to train.