As a Nazgûl, the Witch King had a wide arsenal of powers. Besides from the common Black Breath

As a Nazgûl, the Witch King had a wide arsenal of powers. Besides from the common Black Breath any weapon that struck the Witch-King would be destroyed (a fate shared by Meriadoc Brandybuck’s and Éowyn’s swords), and its bearer would be poisoned. The Witch-King was also a feared sorcerer, having powers over the physical world, breaking Frodo’s sword with just a move of his hand, or weakening the Gates of Minas Tirith allowing the Grond to break them. He was stronger at night time. His power fluctuated over the centuries, with the two peaks of his power being during his campaign against Arnor and in his final battle at Minas Tirith.