Sworn enemy.

I haven't played much as the Sylvan faction; specifically, I completed the Faidaen campaign on "Warrior" difficulty, and that's about it. But while playing, I made full use of the "Nemesis" ability, and I'll even say that I probably wouldn't have been able to do much in the "Greater Vampire" mission without this ability. Three enchanted arrows, hitting not just three enemies, but many more, thanks to the meteor shower – isn't that great? With each turn of the Hero, you can almost radically change the course of the battle in your favor. Of course, you need to take care of the mana, but it's worth it. It's a great ability; I rate it 7 out of 10.