Instructions
Talk to Jona in Port Lfaffan after beating the game. Jona will mention that she has spotted the legendary leviathan in the ocean.
Wait or sleep until nightfall and then head to the beach. Talk to the ghost lady standing near the water. She'll tell you about the equipment she once used to summon the leviathan.
Return to Jona and tell her the news. Jona requests that you acquire the equipment and summon the monster.
Buy, find or make a Watermaul Wand. You can buy one for 4,700 gold in Gleeba or Bloomingdale. Slugly Betsy, abyss diver and python priest monsters drop this item. To make one using alchemy, combine three crimson corals, three seashells and one Stolo's Staff.
Acquire a Flowing Dress. Cumulus hex drops these or you can buy one for 18,000 gold in Upover or Wormwood Creek. Alternatively, combine one Enchanted Robes and three celestial skins to alchemize the item.
Get a Silver Shield for 30,500 gold in Stornway, or make one by combining three mirrorstones, two mythril ores and one White Knight's Shield. No monsters drop this item.
Head the Cuddiedig Cliff and talk to Jona. The leviathan appears. Talk to the monster to start the battle.
Attack the leviathan with moves such as Samual's Kacrack, Pudding's Double-Edged Slash and your Gigaslash power. The leviathan is weak to thunder attacks.
Have one character heal your party each turn. The leviathan's tail swipe damages your entire party at once, and it can kill or severely damage everyone on the team.
Continue attacking the leviathan until it runs out of HP. When the monster falls, the battle ends and you get a fygg.
Eat the fygg to go directly to Sterling's flying train, the Starlight Express. Talk with him to receive his whistle and gain control of the train.
Go to an outdoor location and press "R" to summon the train with the whistle. Alternatively, open your character's inventory and select "Sterling's Whistle" to use it.