Leviathan

The dungeon in which it resides can be entered by passing over Lake Dohr with the canoe and coming into contact with its large shadow. You must traverse a short series of cavern rooms before facing Leviathan. Once the Lord of the Seas is defeated, the party can use the Leviath spell to summon Leviathan and the dungeon can no longer be accessed. Leviathan can cast Protect and Haste, so using Erase is a must. Its Blizzaga can cause huge damage and Tsunami is powerful enough to wipe out an under-leveled party or you in a single hit. Powerful physical attacks, preferably with lightning-elemental weapons, and using Thundaga, will deal heavy damage to Leviathan. Use of a Viking and Provoke may help to divert Leviathan's attacks away from the rest of the party.