Who say's a ghost is a mischievous spirit. There are as many descriptions of ghosts as there are gods. It seems you have a bias.
No bias intended. My casual dismissal of ghosts stems from a basic fundamental belief in logic. It makes no sense and in fact contradicts laws of science built on common sense to believe that an apparition can be formed from matter or energy lost in death. It would be the reorganization of that matter/energy which would constitute a loss of entropy.