The "Mackenzie Poltergeist" is the supposed restless spirit of George Mackenzie, an infamous figure in Scottish history who engaged in merciless oppression of religious minorities, to the extent a portion of the graveyard he haunts is dedicated (somewhat ironically) to his countless victims - it is said to haunt Greyfriar's Kirkyard in Edinburgh and is one of Scotland's most famous and malevolent ghosts.
The Mackenzie Poltergeist is said to cause bruising, bites and cuts on those who come into contact with it and many visitors have reported feeling strange sensations. A schoolboy, hiding in the vault to escape a beating from a master at George Heriot's School, supposedly got trapped here and lost his mind on being confronted by the ghost.
Visitors who take a ghost tour, which has access to the Covenanters' Prison, have reportedly emerged with injuries they have no recollection of sustaining. Even more interestingly, a number of deaths have taken place in the Kirkyard itself, believing the area itself is indeed cursed.