A ghost is a harmless unit in any game. Priests cast exorcisms on ghosts without success but, as , mentioned, they are harmless. The only exception to this is when they go into a tower, where they may get stuck. If the enemy destroys that tower while the ghost still inhabits it, the player may not rebuild it in original position.
Ghost are drawn to castles that have an abundance of statues and shrines, such as headstones or stone crucifixes.