Fergus is pretty tough, and you're pretty much forced to fight him as lvl 2, and he's lvl 4... Took me a couple of tries before I could actually kill him.
Remember to use the pause-button for tough battles. It gives you the time to think things through.
What I did was, I made sure my deathknight had high strength and agility, and I gave him a skill to increase his slashing accuracy. My other guy I gave lots of intelligence, and I gave him a fire missle spell.
Basically, you have to get your Deathknight in front to start attacking, while your other guy casts as much fire spells as possible. Don't forget to use mana potions and health potions, or regeneration potions if you actually found any.
Tovi 
