[Endoperez]

I used the settings included in your quote:

"I tested it, with a commander that had 1 str, 25 attack, 0 defense and a weapon with -10 damage, damage cap 1, 25 attack against random indies. According to log, all attacks were repelled."

In other words, I changed Commander of Ulm to:
str 1
attack 25
defense 0

and forged him a Sword of Sharpness, which I had modded to be:
damage -10
capped at 1 damage max
attack 25
defense -10
huge length, I think I used 7

This produced a unit with:
attack 50,
defense 0,
weapon long enough to repel spears and
total damage (str + weapon) -9, incapable of dealing damage