Lamprey

Lampreys are repulsive, leechlike eels of deep salt and fresh water, with round sucker mouths ringed by sharp teeth and sickly brown, green and gray skin, grayer in the sea.

After its first bite, a lamprey drinks blood each round thereafter at 2 hit points per Hit Die, so an ordinary lamprey drains 2 per round. Only killing it pries it loose; otherwise it lets go once it has drained hit points equal to its own. A giant lamprey's victim bleeds 2 hit points per round afterward until bandaged. Sea lampreys save at -2 against fire, though fire aimed at an attached lamprey forces its victim to save as well.

Lampreys lair in deep-water caves or coral and range up to two miles away thanks to perfect homing. They feed where they catch prey, so lairs hold no treasure, only 4d6 eggs, which these savage, territorial creatures defend fiercely.

Sharks relish giant lampreys, which may draw sharks away from coastal communities.

This air-breathing mutation of the sea lamprey is about 3 feet long, thick and heavy, and light to blackish green, hiding in tall grass or brush 75% of the time. It slithers like a snake through most climates except desert and extreme cold, preferring dark, damp places and small caves. Its bite deals 1 point, then it drains 1 point per round for three rounds unless killed or removed. Each one clinging to a character counts as 1 lost point of Dexterity. Killing it or applying fire, which makes it let go, are the only ways to remove it.