Here's the "one of these things is not like the other" leftover undine we decided to rename "ondine" to avoid confusion.
UNDINE
FREQUENCY: Very rare (uncommon on Elemental Plane of Water)
NO. APPEARING: 2-20
ARMOR CLASS: 6
MOVE: //12.
HIT DICE: 2
% IN LAIR: 80%
TREASURE TYPE: P, R, any two magic
items (20%)
NO. OF ATTACKS: See below
DAMAGE/ATTACK: See below
SPECIAL ATTACKS: Rapid drowning, paralysis
SPECIAL DEFENSES: Invisible in water, plane shift
MAGIC RESISTANCE: Standard
INTELLIGENCE: Low
ALIGNMENT: Neutral evil
SIZE: S(3. long)
PSIONIC ABILITY: Nil
Attack/Defense Modes: Nil
LEVEL/X.P. VALUE: IV/163 + 2/hp
These creatures come from the Elemental Plane of Water. Like water weirds, they enjoy drowning their victims; it is also believed that they survive by draining the lifeforce of their victims. In appearance, undines are similar to miniature merwomen; they have a single, scaled, lateral tail (much like that of a dolphin) which is connected to a humanoid upper body.
Their lairs are simply areas of water which they use as a base for traveling between planes, This area is found along a well-traveled route, populated seacoast, or any other area which offers a great number of potential victims. As a result, many bodies often litter the floor of the lake, river, or ocean that they inhabit.
Undines have the ability to charm monsters as per the spell, usable once per day. By doing so, undines can command larger sea creatures (whales, giant squids, or octopi) to do their bidding. Undines use these larger creatures to destroy ships or whisk sailors from decks. Once in the water, these sailors are then attacked by the undines, who attempt to slay them. During this time, the other creatures do not attack as the undine must kill the victim themselves in order to consume their lifeforce. An (invisible) undine grasps a person on a successful to-hit roll, which causes the victim to save vs. paralysis or become completely paralyzed. The victim drowns in 1-2 rounds, even if able to take a deep breath before going under. Undines are not strong, so a mobile character can easily escape from one’s clutches.
Undines are naturally invisible in water, even if attacking. If an undine is losing a battle, the creature flees for its lair. Characters attempting to locate an undine must use magical means (spells or devices) to do so. In extreme cases, as when the undine’s death is the probable outcome of combat, this creature may use its ability to transport itself back to the Elemental Plane of Water if no other means of escape is available. This plane shift ability works once per year, so they are reluctant to use it.
Originally appeared in Dragon Magazine #116 (1986).