Well, I think the hardness, sharpness, etc, would directly determine how much damage a foe takes (barring spells and special abilities that induce immunity, healing, etc).
Before we go further, though, do you figure we ought to just turn this into a D&D campaign, with a hugely expanded mythical critter base, or do you prefer to devise your own system?
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)