She appears to be based on a Slavic water spirit and is also a sorceress who 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 Confodere glyph, as she is vulnerable to Slash damage, and you'll have plenty of time to dodge one of her attacks. Arcus will deal less damage, but is a safer strategy. 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.
Another strategy is to use Arma Chiroptera from the top of a Moai and continuously fire bats at her, only getting down when she calls a tsunami or changes her hair to a water pump. 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, because the damage of the pounding waves is enough to kill you on one hit (even to a lv. 255 Shanoa). This fight will take a while, but with patience, you will beat her.
|Item Data: Rusalka|
|Image||Name - Game|
|Type / Users||Attributes / Consume||Statistics / Sell||Found||Notes|
|Medal awarded for defeating the water demon, Rusalka.|| Item (Boss Medal)|
|Sell: (cannot be sold)|| Drop: Rusalka|
Conditions: Defeat Rusalka without taking damage.