You will face the monster Leviathan at the end of Tywll Cave in the Nintendo DS game "Dragon Quest IX: Sentinels of the Starry Skies." Leviathan attacks Mayor Bryce and Jona at Cuddiedig Cliff, forcing you and your party to fight him. Leviathan is a very strong monster, considering your party members' experience; they should be around Level 19 at this point in this game. This is a long fight; keep your party's health up as you attack Leviathan to outlast him.
Restore all of your party members to full health with Medicinal Herbs before you step into battle with Leviathan. Move forward toward the monster once you are at full strength to begin the battle.
Cast "Buff" on your party members to increase your defence. Your party's Priest will have this spell after learning it at Level Eight. You can cast it only on one party member per turn, but the spell lasts the entire battle for each member.
Cast "Sap" on Leviathan to drain his defence; your Mage will have this spell. You may need to cast the spell twice before it affects Leviathan.
Attack Leviathan with your best abilities on each turn; use "Attack Plus 10" for a party member with a sword and "Propeller Blade" if you have a member armed with claws. Your Mage should attack with the "Crackle" spell.
Heal your party members with the Priest's spell "Midheal," especially after Leviathan attacks the group with "Tidal Wave" or "Massive Swipe." Don't let any party member's hit points drop below 30, because "Tidal Wave" can then finish them off.