To follow your pos., neg. theory. Any chi that is not used to heal or nurish a body would fall under Adverse chi, which is neg. As all chi is programmed by the mind (Shen leads the Li which leads the chi, Spirit leads mind, mind leads chi). As to address the iron shirt or body technique, To guarentee victory, avoid battle. But if battle is unavoidable, then take a close look at how the iron skin works. If the iron skin is focused chi, break the focus. Meaning before the battle distract his mind, break his focus. From quick talkin to jumpin around like a fool, then leaping into a skilled attack, you may catch them off gaurd and incress your chances of landing a sucessful strike.
As for the dark chi, just remember the longer you look into the abyss, the longer the abyss looks into you.