King of the Dead vs Witch King

[Boromir88]

if they actually did fight the Witchking would have one because like the prophercy said that no man could kill the Witchking the King of the Dead even though being dead he was still a man~The Failed King

Actually the prophecy says that he would not be killed by a man. The prophecy is made by Glorfindel, and he says:

Far off yet is his doom, and not by the hand of a man will he fall.'~Appendix A: Gondor and the Heirs of Anarion

This is basically Glorfindel looking into the Witch-King's future, to put it that way, and prophecying that a man would not kill him. It doesn't say that a man 'could not kill him' but that he would not be killed by a man.

If The Witch-King could not be killed by a man, he would not have feared Boromir I:

Boromir son of Denethor (after whom of the Nine Walkers was later named) defeated them and regained Ithilien. But Osgiliath was finally ruined, and its great stone-bridge was broken. No pepople dwelt there afterwards. Boromir was a great captain, and even the Witch-King feared him.~Appendix A: The Stewards

Why would the Witch-King fear him, then if he couldn't be killed by a man? Note: this isn't Boromir of the Fellowship, but Boromir I the Steward.

1,000 Reader, yes I think the effectiveness of the Dead Army we have debated to death, and there's nothing more to add.