It's a good idea to give them a sling to use. The magic they possess will be weak at first, and they are very quick to die in battle. Each attribute will be assigned between a 3 and an 18 in score, though you rarely see less than 7 on anything. Your two key fighters should have 18's on their strength, dexterity, and constitution. Nothing else really matters for them, so cut them as low as 9 on each of their other attributes.
Dexterity improves the chance of ducking an arrow.
If you're wondering, there is NOT such a spell. However, if Mandark survives to higher levels, he will have access to several spells that may as well be called such. Believe it or not, this fog works to your advantage. The more creatures you can see, the more you are seen by. It is better to pick one off at a time than to be swarmed by a horde.