Rusalka

Castlevania: Order of Ecclesia
Rusalka appears in Somnus Reef as the game's 5th boss. She appears to be based of a Russian water spirit and is also a sorceress that has total domination over all the water in the area, making the room an ideal battleground for her. The best attack strategy to use here is to use the Vol Confodore glyph, as she is vulnerable to edged damage, and you'll have plenty of time to dodge one of her attacks. Although she is also weak to thunder attacks, it may be better not to use them, unless you are willing to use the Weapon+Thunder Glyph Union attack. Vol Fulgur does not do as much damage per strike as edged weapons, although it can strike her from atop the moais. Her attacks consist of her using her hair as a whip to attack you at close range, turning her hair into a water pump to spray jets of water at you, firing a wave that erupts into a geyser when it reaches or gets below you, or dropping moai stalactites on your head. As long as at least one moai is still intact, she may yell out "Maelstrom!" or "Waves be wild!". At that point, you must get underneath one of the moais to dodge the attack. This fight will take awhile, but with patience, you will beat her.