Oh, Vilk
That quest reward is completely random. In my case the reward there was some stupid spell like berserk or something. I remember it clearly, because up until the islands I had only healing and resurrection as useful spells. No gift, no sacrifice, no magic spring, no nothing.
I disagree about fear though. If the enemy breaks through the barricade, your dryad/sprite goes to charge any skeleton group she sees, even if it's not within the fighting range. That's a severe problem, because you don't want to have weak units run into the middle of the enemy lines just like that. They get minced in just one turn by the zombies and the black knights, and on impossible, karador's units just LOVE to crit - especially the black knights who even have it as a skill.
BTW, the battle is very different from normal and hard difficulties. On normal and hard you can do it with a powerpuff girl army just because you'll have a serious strength in numbers and your spirits will be leveled beyond 25 at this stage, and you will be 26+ level in any case.