A long time ago, much longer than the first known holidays of yore, there was a powerful demon calling himself "Nightmare". He was stronger than the greatest warrior alone. He traveled from one world to the next bringing chaos and destruction with him.
Then one day, the greatest warriors of each world that had suffered from the demon's power came together and banished the creature into a mystical stone. The warrior of the world in which the creature was captured was a person named Jack. He vowed to keep the creature contained within his world and to keep his power from becoming a threat again.
The warriors still feared the creature, and decided to seal their worlds from Earth. Eventually each began to ease up a little, and allowed their magic to seep into the world one day a year, creating the holidays.
Halloween however, suffered dreadfully. Their world became slowly more and more harmed by the creature's power, and became a realm of darkness and fear. Jack had become a living skeleton, and the citizens walking monsters, like the demon that caused it.
And so the demon slept for thousands of years…
Until someone releases him.