Use triggers.
You just need to damage formula, attributes and bonuses and you're good to go. Although if you aren't experienced with this, move along.
maybe make a periodic of this unit attacking a dummy, and setting the damage dealt into a variable, and by that damaging the others? This really isn't so effective.
We'll just calculate the hero's damage it can do and damage units with a random amount based on those calculations.
Now, a hero's damage done is based on his primary stat, damage dices and bonus items such as claws.
Damage: (Base damage + Amount of Dice) -> (Base damage + (Amount of DicexNumber of Sides))
Save the units damage bonus gained from items and abilities in a real, we'll call it [Bonus Damage], only items like claws (bonus damage) not stats like boots of argility.
Afther that save the hero's main atribute (argility, strenght or int) in another real, include bonusses, we'll call it [Base Damage].
Now search the units 'Attack - number of dice' and 'Attack - Number per dice'.We'll save these two things in a real called [Attack - number of dice] and [Attack - Number per dice].
'Set [Total Damage] = (Random number between ((([Base Damage] + [Bonus Damage]) + [Attack - Number of Dice])) and (([Base Damage] + [Bonus Damage]) + ([Attack - number of dice] x [Attack - Number per dice])))'
Please keep in mind that this is all hand typed and I don't have a World Editor here at the moment.
Now if for example the hero has Command Aura increasing the total damage by 10% add something like:
'Set [Total Damage] = ([Total Damage] x 1.10)'.
I know this isn't exactly the amount of damage the hero would've done, but it's close enough I think.
Please let me know if this was unclear, haven't got much time to tpye a long story and I don't have World Editor with me here. These are just the calculations for damage.