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Olhydra is an archomental in the Dungeons & Dragons fantasy role-playing game. Her symbol is a blue-green square. It is possible that Alyolvoy, an evil archomental of water mentioned in Dungeon #37, is an alias of Olhydra.
Olhydra first appeared with the elemental princes of evil in the original first edition Fiend Folio (1981), created by Lewis Pulsipher. Olhydra was one of the main antagonists in Frank Mentzer's 1982 RPGA module The Egg of the Phoenix, which was later included as part of the expanded 1987 adventure compilation, Egg of the Phoenix.
Olhydra appeared with the evil archomentals in the second edition book Planescape Monstrous Compendium Appendix III (1998).
Olhydra appears as an endlessly breaking wave of water, an amorphous blob with almost-human features buried within its depths. She is about 20 feet wide and weighs 5,000 pounds. She may also appear as a feminine, half-human and half-pleiosaur creature with tentacles for hair and a semi-transparent liquid body.
Olhydra harbors an intense hatred of Imix and schemes to destroy him. Along with Imix, Yan-C-Bin, and Ogrémoch, she once pursued the artifact known as the Egg of the Phoenix. One of her greatest allies is Dagon, and rumor has it that she and Dagon may have spawned twin daughters. She occasionally comes into conflict with Blibdoolpoolp, Eadro, and Persana, but gives little thought to Ben-hadar.
Olhydra is served by undead dinosaurs, kapoacinths (aquatic gargoyles), evil water elementals, water grues, water mephits, orlythys, renegade hezrou that she's lured away from Demogorgon, tojanidas, callers from the deep, and lesser water weirds. A triad of sea hags known as the Blue Coven also serves her; the three have merged into an entity with three bodies and a single mind.
Olhydra lives in the ruins of a castle made of living black coral, submerged in a great indigo lake, on the Elemental Plane of Water.
Olhydra's faithful include aboleths, sahuagin, scrags, anguillians, sea hags, krakens, seawolves, eyes of the deep, and many more. Pirates, wicked sea druids, and mariners flock to her cause, and she has one of the biggest followings among the evil elemental cults.
Those of Olhydra's clerics who wear clothes wear robes with blue trim. Many carry around small jugs of sea water for the purpose of special ceremonies and blessings.
- Shel, Mike. "The Mud Sorcerer's Tomb." Dungeon #37. Lake Geneva, WI: TSR, 1992
- Turnbull, Don, ed. Fiend Folio (TSR, 1981)
- Mentzer, Frank. The Egg of the Phoenix (TSR, 1982)
- Mentzer, Frank, and Paul Jaquays. Egg of the Phoenix (TSR, 1987)
- Cook, Monte. Monstrous Compendium Planescape Compendium III (TSR, 1998)
- Jansing, Eric, and Kevin Baase. "Princes of Elemental Evil: The Archomentals." Dragon #347 (Paizo Publishing, 2006)
- Cook, Monte. "Four in Darkness: A Guide to Elemental Evil." Dragon #285. Renton, WA: Wizards of the Coast, 2001.
- -----. Return to the Temple of Elemental Evil. Renton, WA: Wizards of the Coast, 2001.
- Cook, Monte, and William W. Connors. The Inner Planes. Renton, WA: Wizards of the Coast, 1998.
- Grubb, Jeff. Manual of the Planes. Lake Geneva, WI: TSR, 1987.
- Grubb, Jeff, Bruce R. Cordell, and David Noonan. Manual of the Planes. Renton, WA: Wizards of the Coast, 2001.
- Jacobs, James. "Spawn of Elemental Evil." Dragon #285. Renton, WA: Wizards of the Coast, 2001.
- Jansing, Eric, and Kevin Baase. "Princes of Elemental Good: The Archomentals, Part II." Dragon #353. Bellevue, WA: Paizo Publishing, 2007.
- Kestral, Gwendolyn, et al. Monster Manual IV. Renton, WA: Wizards of the Coast, 2006.