Leviathan's physical attack is Water-elemental, and may also cause Instant Death. Leviathan is weak to Fire.
Initially, Leviathan only has one arm. When it is "broken" with sufficient damage, a second arm will join it, repeating until there are four arms. When all four arms take sufficient damage, Leviathan flips over into its true form. At this point, it can attack up to five times per turn (once per arm and the main body). Leviathan will also begin casting magic at this point. It will also start charging Tidal Wave, but doing a significant amount of damage will break this attack.
The party should include an Elementalist to deal with Leviathan's magic and buff the party's attacks, and equip Ice Shields. Fire-elemental equipment and abilities from jobs like Black Mage and Spell Fencer are useful.
Leviathan can be difficult because of its frequent attacks and chance of Instant Death. A White Mage may be advisable over a Salve-Maker due to the greater healing of Raise over Phoenix Downs and being able to re-cast Lux more frequently.
Leviathan (Biblical Hebrew לִוְיָתָן or לווייתן Liwyāthān) is a violent sea creature that is referred to in the Hebrew Bible as well as the Talmud and some other ancient Jewish texts. During the golden age of seafaring, the term Leviathan became synonymous with any large sea creature, sometimes describing whales. Bible scholars interpreted Leviathan to be either a demonic sea creature and an enemy of God.
The Talmud and other ancient Jewish sources refer to Leviathan more specifically as a sea serpent, sometimes with multiple heads capable of breathing fire, that was made on the fifth day of Creation. It is said that during the end of days, God will make tents, or sukkah, out of the skin of Leviathan for the righteous to live in. Some have speculated that Leviathan was based on a real animal, the most popular theory being the Kronosaurus and the Nile crocodile.
Being mentioned in the Final Fantasy series as the King of the Seas, its incarnation also appears to derive from the legends of the Shinto god Ryūjin or Owatatsumi, said to be the dragon god that reigns over the tides and the seas. This is further reinforced by the parallels of the Leviathan faith of Wutai in Final Fantasy VII, as Shinto also sees the worship of water dragon kami in Japan.
In some cultures it is believed Leviathan lives at the bottom of Mariana Trench.