the Druedain and the power of the Watch Stone

[Finwe]

Gwaihir, it was not the Stone of Erech that kept those ghosts "alive," it was Isildur's curse. He cursed them to be trapped there until his heir summoned them to fight against Sauron, and that was what they were waiting for, Aragorn's Ride. The Stone of Erech was merely a symbol, not the reason.

As for the Elves and Gondorians, I wouldn't call them magical, per se. I just think that they have a very close affinity with nature. That was how the flood was called up at Rivendell. That is also how Orthanc and the Outer Walls are so impregnable. The Gondorians had those skills because they learned it from the Elves. I wouldn't necessarily call it magic.

As for Merry's sword, perhaps it was magic, or perhaps it was the little Hobbit's stout, pure heart that wounded the Witch-king more. I personally think it was more of the latter. Anyone can wield a blade, but when it is the hands of one both stout and pure of heart, then there is an opponent worth fighting.