KELPIE

Kelpies are a form of intelligent aquatic plant life that, in their own shape, rather resemble a pile of wet seaweed. They are able to shape their bodies into any form they choose, and will often assume the aspect of a beautiful human woman in order to lure men into deep waters. They have also been known to take the shape of a horse. However, though the form may be changed, the substance still resembles green seaweed and the effect is somewhat grotesque.

To counter this, the kelpie can cast one powerful charm spell per day. If the victim does not save against Spells (at -2) he will perceive the kelpie as the most wonderful, perfect and desirable woman (or steed, perhaps) and will willingly leap into the water to join her (or gain it).

The kelpie will wrap itself around the charmed man, he will attempt to inhale water and sink with the kelpie in an ecstasy of drowning. If left alone, he will happily drown and be dragged off to the kelpie's lair to be consumed. Even if the kelpie cannot physically reach the charmed victim, he will still try to swim downward and breathe water. 

Charmed victims attempting to drown themselves will suffer 2-20 hit points of damage per melee round until they either surface for air or perish.

If the charming kelpie is killed, the spell will be broken immediately. 

For some reason, females are immune to the spell of the kelpie.

Due to their slimy wetness, fire attacks do only half damage on kelpies (none if a saving throw is made).

Legend has it that [...] because kelpies were created by the sea-god as punishment for those men who are rash enough to sail the oceans without paying their lord his proper respect. Women were not involved in these transgressions and thus did not incur the sea-lord's ill will. Others say that Olhydra, the Elemental Princess of Evil Water Creatures, created the kelpies and rendered females immune in proper regard for her own gender.

Besides the oceans and the seas, kelpies will also be found in dismal swamps and stagnant subterranean grottos; occasionally they will be found in almost any deep body of water, even man-made. 

They can leave the water to walk on land for short periods of time (1-3 hours maximum).

Kelpies are very cunning and will try to pick off stragglers, lone watchmen or tail-end members of groups if at all possible.