ok here is what i suggest (and will approve)
xx ap xx mp cost= min damage (total of ap and mp cost) max (min damage x2)
low min, and high max. there is a big window for damage in there, but as if the same with real grenades, you might get a few scratches, you might have your torso severed. It think the damage reflected by the grenades with low min and high max,is a good representation of the real effect of grenades. Later you will have stronger grenades, higher ap and much higher damage, but those will also have much higher requirements to create.
Crossroads {A unique Final Fantasy}[Working Title]