A good army to beat Karador on impossible with a paladin?

[Vilk]

The book is the book of the Necromancer lost city. Magic School offer this quest then you have to ask to the old which that throws you to a tomb magically sealed in the swamp cemetery. In this book when you use it you get the Necromancer scroll.

EDIT: I also agree that it's one of the easy fight once you get it in the right way. I haven't tried yet in impossible (still polishing my play during previous parts for a better time record) but I suspect it will be still a fight more easy than other.

EDIT2: About fear, if the enemy hero lost time to cast this that's not a bad point for you, just cast dispel right before it will the turn of feared unit. Anyway Dryads aren't useful during first parts of the fight but more later. With Royal Thorn you won't have this problem... At this point of the game Royal Thorn suck a little but that is true too for Dryads in the area.