- How to defeat Galtran?

Galtraan, like any Necromancer, can be defeated using Diplomacy. Let him breed his skeletons, and we'll use other monsters... and then it's a fight to see who wins... it depends on how lucky you are with the monsters. When playing on a random map, you can place strong monsters, and it's debatable who will have to worry about saving themselves... as they say, "it all depends on how the map turns out."
Personally, I'm against using skills like Diplomacy and Necromancy; I think many will agree with me... but when playing "however you want," it's a perfectly viable option.