I was re-watching the movies and kept hearing that "no man can kill the witch king". I am wondering if this is true or was it basically the Witch-King bragging. Did Éowyn sneaking into battle actually win the battle?
closed as primarily opinion-based by Möoz, Jason Baker, Himarm, Wad Cheber, KutuluMike Feb 15 '16 at 3:32
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At that point in the movie, the Witch King is probably bragging, as all bad guys should do in a movie when the good guy is almost but not yet dead. It is however based on some truth. Long ago, Glorfindel had prophesied the defeat of the Witch King, who had probably heard of the prophesy in the long years since:
"He will not return to this land. Far off yet is his doom, and not by the hand of man will he fall." - The Return of the King, Appendix A (iv)
The rest of the answer is partly of my own argument: The prophesied "hand" that will bring about the Witch King's downfall is not of Eowyn, but of Merry.
After all, is it not by the hand of Merry that the dark wards protecting the Witch King were dispelled, after which pretty much anybody can kill the Witch King? Merry's blow was the crucial one - Eomer could have replaced Eowyn and the Witch King would still be dead.
That said, we can also say that it was Tom Bombadil (not a man) who gave Merry (not a man) that enchanted blade, and it was Eowyn (not a man) who brought Merry into battle and then unwittingly distracted the Witch King (a man) from noticing Merry.
Edit: I read from an answer on another question here that an analysis suggests only Eowyn - a woman - is light enough to carry Merry into battle on a horse (remember in the movie Merry couldn't get his own horse moving) because a man and Merry combined would be too heavy for a horse. In that sense, you can argue that Eowyn's sneaking into battle is necessary to bring Merry there - otherwise who else in the Rohirrim wields an enchanted blade? It's not by Eowyn's hand, but by her weight, that Merry's hand can be present in that battle at all.