Halloween has its roots in Samhein, the Celtic New Year which began with the night of death. During Samhein, ghosts, demons and other fallen beings walk the land... the day when the dead crossed into the realm of the living in search of human hosts whose bodies would give then life for the coming year.
To stave off these ghosts and demons the ancient Celts carved scary faces into gourds which were then lit with candles, scary masks were worn so the living could pass as demons and treats were passed out in an attempt to appease the hungry dead.
All village fires were doused on the night of death. The only fire left burning was kept in a central druidic sanctuary. his fire was then brought to a local village bonfire, where the local druidic high priests held vigilance. Living humans were placed in these bonfire as human sacrifices, then... when the Sun rose on the Celtic New Year the fire of human sacrifice was used to re-light the fires in the homes of the villagers.
It seems that Halloween's ghosts and creepiest creatures did not just appear out of thin air ... most have been instilling real fear in the mind of man for a very long time.