Leviathan is a boss that guards Istory Falls in Final Fantasy V that protects one of the four ancient tablets, but the party does not need to fight it as soon as they recover the tablet; they can return later for the battle. Conquering Leviathan nets it as a summon.
Leviathan's strongest attack is the Tidal Wave, which can be absorbed with Coral Rings. Leviathan can also paralyze a party member, and cast Aqua Breath. As with many water-themed monsters, Leviathan has a Lightning vulnerability.
The party's Blue Mages can learn Aqua Breath when hit by it.
With Coral Rings equipped, the party only have Leviathan's physical attacks to worry about. Coral Rings (available in the Phantom Village or won from Yellow Dragons in Exdeath's Castle) will make the fight easier, but are not necessary. Casting Mighty Guard helps. Thundaga is effective, either as a spell or combined with Spellblade.
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.