Is there a way to find hidden treasure of pirate lord?

[Gatts]

The key is blood of his enemies (he got real funny name) and you can find him on the same map - attack him win, get XP, Money and I think even some artefact.

You can buy a scroll of "lighter than water" or something like that from local mage - than just search for part on the map where houses are under water and sail there for a while - the scroll will work automatically - you will be asked to use the scroll and voila-black gold ship is above water - you will get some reward and be able to buy undead army from that ship.

About the ever-in undead at night-changing ship - if you will fight them at night - you will get some XP/Money, but I advise to return when they are in "human" form, get them the right stuff from the temple and this way you can get more XP and Money...