Nereids are transparent and invisible in water. On land they appear as young, slim and beautiful human women. They are playful and capricious, but few (10%) are actually evil. An equally small number are good. In extremis they can attack with their spittle (range 20-ft) that blinds its target for 1d12 rounds, but they can also control the water of their homes, speeding or slowing swimming movement through it (up to double normal speed, or down to 25% of it), causing crashing waves that deafen, prevent conversation and interrupt spell-casting, or forming miniature waterspouts that attack as 4 HD monsters (inflicting 1d4hp damage—no more than one such waterspout per nereid per round).

Males of any human, demi-human or humanoid species cannot harm a nereid at all. They will be infatuated with the nereid (no save) and seek to woo her. A man can try to catch the nereid—but she will turn to water and flow away from his embrace 50% of the time. If caught and held, she will kiss him, in which case he must save vs poison or drown.

A nereid will always have a diaphanous shawl that contains her soul. Anyone holding the shawl can control her; she will obey their commands out of fear, even if they are male. A nereid will do almost anything short of physical violence to regain her shawl.