It is unkown what the true origins of the Giant Jack-O-Lantern, but It may be in fact that Marnie Piper could have been the true creator of the Jack-O-Lantern. Due to the fact in Return to Halloweentown she created one that she gave to Aggie when she was about to leave Cromwell Castle. This can be explained by the the Novikov Self-Consistency Principle. This theory of time-travel, stating that "Nothing can be changed because anything a traveler does merely produces the circumstances they had noted before traveling," This similar theme can be found in the Harry Potter series via Time Turners. Though this can also cause some inconstistencies with the rests of the films.