Black Water comes from the Elemental Plane of Water, near the edge leading to the Negitive Energy Plane. It craves the energy of the living, and seeks it out with a uncaring vengance. They appear as dark oily blobs in the middle of a large body of water. A closer look will see a swirling yellow energy deep inside the oily blob before it attacks.
Overturn (EX): A Black Water can be a serious threat to a ship that crosses its path. The Black Water can easily overturn small craft (5 ft. of Length per HD). Even large ships (20 ft. long per HD) Can be slowed to half speed.Drench (Ex): The Black Water's touch puts out torches, exposed lanterns, and other open flames of nonmagical origin if there are Large Size or smaller. Black Water can dispel magical fire it touches as dispel magic cast by a sorcerer who's level equals the Dark Water's HD.
Improved Grapple: If the Black Water succesfully hits with two Pseudopod, or someone jumps into it, it makes a immediate Grapple Check. If failed, they are grappled, and next turn the Black Water will attempt to pin. Those Pinned start to fall subject to Drowning rules, as in the DMG.
Elemental (Su): Immune to Poison, sleep, Paralysis, and stunning. Not subject to critical hits.