She is encountered the first time inside the Underwater Temple. She likes to cast Water on a single member or the entire party. She can also casts Toad or Mini, which may slow down the team. Discharge can inflict Stun on all members. Undine Cry is her best shot. It will inflict about 500 damage to the entire party, plus Sap.
Remember to heal regularly, or at least have Eduardo cast Aiding Anthem. It will hardly hit all of them at the same time but still can be quite dangerous. She is weak against Lightning, so Judgment Bolt or Thundara works well. Also, equip the Warrior with a Coral Sword and attack her with Strike. It will do a lot of damage. If the Player has a Dragoon, use Boost Jump while equipped with Coral Sword to deal 1000+-1400+ damage
This battle occurs when the party tries to leave the Underwater Temple. It is a scripted battle.
This battle by default cannot be won. After a certain amount of time, whether party members attack Styx or not, Styx will cast Lorelei's Tears, which reduces all characters' HP to below 10. Afterwards, she'll get hit by a cannonball and the battle ends.
This battle occurs inside Castle Burtgang, when the Warriors of Light enter the throne room. In this battle, Styx will use various attack which can harm the party badly. She will attack with Water, Waterga, Undine Cry and Lorelei's Tears. Waterga can deal about 1500 damage to a front-row member or about half of it to all members. Water will deal less than that and Undine Cry will damage all allies just as Waterga but it will inflict Sap. When her HP get lows, she will cast Lorelei's Tears, which basically means casting Waterga continuously on every character. Beside damaging your party, she is capable of casting some other spells. She may dual-cast Mini and Toad. She can also counter Lightning-based spells with Discharge to Stun all allies, but it shouldn't affect all members. She can also use Temptation or Siren Song to cause Confuse or Silence to all members, but they usually miss. She can also can Haste on herself when her HP is getting low.
First, make sure the Unicorn is acquired before entering this fight. Players may want to cast Shell on every character at the start of the battle to reduce Styx damage as her attacks are all magic-based. She can damage you a lot with her spells but Shell and Unicorn's healing will neutralize that. Also. Unicorn will blow Temptation's effect away. Mini and Toad is not a real threat here as they can be removed easily. This fight doesn't have to be rushed anyway. Siren Song can cause Silence and it can hit your main healer and must be gotten rid of it immediately. When her HP gets lower, she will cast Haste and Lorelei's Tears. Lorelei's Tears can do heavy damage, so the party should be kept in good shape. This fight won't be very hard, especially when Vata was encountered a while ago.
While Styx is faster and more powerful, she used the same strategies from the previous battle. Waterga, Undine Cry and Tidal Wave can inflict major water damage to the party. Siren Song, Temptation and even Undine Cry can inflict several statuses to the party such as Confuse, Toad, Mini, Sap (status). Lorelei's Tears can damage twice as much as Undine Cry.
This fight is pretty straight forward and it will be faster if the party is highly leveled. A White Mage, Seer or anyone with Esunage should be enough to deal with negative statuses. Keep the party HP above average while attacking her with powerful spells or F-abilities.
Styx is a river in Greek mythology that formed the boundary between Earth and the Underworld often called Hades which is also the name of this domain's ruler.The