Don't bother fighting him; he's incredibly lucky, you won't win anyway. For example, I assembled an army, freed Duncan, and quickly headed to the castle, while hiding Duncan in the church, which is nearby. I stayed in the castle, building up my army. This stupid undead guy kept wandering around near my castle but didn't attack. But when I took Duncan out of the sanctuary, he immediately rushed over. He just kept going back and forth. Meanwhile, my castles started getting captured. I went to the port castle; it had two garrisons. It's better to take the one that's closer to the enemy (because they won't go through the far one; they're not that stupid). You take the garrison (if you don't have enough troops, you'll suffer heavy losses). Andreas will immediately come after you. Quickly capture the port castle and stay there. Then, build a shipyard. You don't need to bring Duncan out, although you can use him as bait. Get on the newly built ship, and an enemy ship with a good army will sail towards you. It will start a battle and immediately retreat. Mission accomplished! =)"