Durza

Eragon remembered it vividly. “Murtagh shot him twice. The first arrow caught him in the shoulder; the second one struck him between the eyes.”

“I was afraid of that,” said Ajihad, frowning. “You didn’t kill him. Shades can only be destroyed by a thrust through the heart. Anything short of that will cause them to vanish and then reappear elsewhere in spirit form. It’s an unpleasant process, but Durza will survive and return stronger than ever.”

Eragon, Ajihad, pg 590

He lunged forward . . .

And stabbed Durza in the heart.

Durza looked down with shock at the blade protruding from his breast. His mouth was open, but instead of words, an unearthly howl burst from him. His sword dropped from nerveless fingers. He grasped Zar’roc as if to pull it out, but it was lodged firmly in him.

Then Durza’s skin turned transparent. Under it was neither flesh nor bone, but swirling patterns of darkness. He shrieked even louder as the darkness pulsated, splitting his skin. With one last cry, Durza was rent from head to toe, releasing the darkness, which separated into three entities who flew through Tronjheim’s walls and out of Farthen Dûr. The Shade was gone.

Eragon, Battle for Furthen Dur, page 632