Main Quest - Expedition
End boss is the Bar Lodos
Starting difficulty is Normal 18 and Up (Multi-party quest 12)
No level restrictions
This boss tends to keep his distance as you're on a unique stage for battle.
On the back of the ship you are riding is a Harpoon gun, wait for Bar Lodos to pop up dead center of the front of the ship and you can spear him and pull him down.
This allows you to preform some heavy damage with melee attacks as he won't be as far away from you.