Zeitgeist

Though similar in nature to a poltergeist, the zeigeist is in fact the spirit of feeling at a certain time, this would almost certainly make the Charles Dickens tale 'A Christmas Carol' a more realistic premise as it includes not one but several zeitgeists. The ghost of christmas past, the ghost of christmas present, and the ghost of christmas future all of which come with terrible news. Under no circumstances engage in conversation with a zeitgeist of any kind, and if needs force this to happen make sure you bring with yourself a copy of The Philosophy of Time Travel. This book alone should scare the pants of anything which has no regard for the nature of time and the impacts had by travelling in a non-linear path through it.