The Balrog vs The Witch King

[CSteefel]

Well, take the breaking of the Gates of the City on its own value then, it is an impressive display of force, and as I believe you said, indicates clearly the augmentation of the WK's power.

Otherwise, I agree it is difficult to say how this would play out against a Balrog, since there is ample evidence that the WK was overmatched at various other times, although he seems to have recognized it when this was the case and he withdrew. So it is quite possible he would do the same when faced with a Balrog.

The other possibility that I would not completely discount is that the WK on the Pelennor Fields is not completely aware of the power of some of the players on the field at that time. Gandalf is the obvious one--how would he have known that Gandalf had been sent back, although perhaps others will dispute whether his power is really augmented. In the end, of course, the WK is defeated by Merry and Eowyn, certainly something he did not count on.