A canoptek wraith attacks a group of imperial guardsmen]] While most of the necrons when into their slumber aeons ago, the Canoptek Wraiths patrolled the ancient crypts of their tomb world. The most notable feature of Canoptek Wraiths is its dimensional destabilisation matrix, which was originally intended to be used to reach into machines and repair them without removing their casing and components. However, these matrixes can also be used to great effect when dealing with the upstart life forms of the galaxy. When in combat, these matrixes allow the wraith to phase its claws and tendrils into the opponent, completely wrecking him from inside. In a battlefield, canoptek wraiths can also use their matrixes to move across any kind of terrain without pausing by phasing out.
Wraiths - This article discusses the 3rd edition wraith.
Codex Necrons (5th edition), p. 44