Okay so you're really pissed off that you can't beat the witch king because you aren't anywhere near perfect mode and you don't have a morgul decay right? Well, what you can do is use another item called rusts of moria which reduces the witch king's armour but not entirely. Use Idrial's aura of the valar and power of the valar to revive other characters, use berethor's defensive strike so the witch king doesn't counter attack and use any of elegost's attacks. Than once u are on perfect mode use banner of elendill which will make the witch king unable to counter attack, for a very long time now use berethor's ecthelion wrath and switch characters from elegost to either hadhod or eaoden. Use eaoden's enraging blow and wrath of edoras or with hadhod mountain rage. Eventually the witch king will start to counter attack again just repeat what u did before and he will be dead in not time