What if when Silver Shamrock were making mask they produced Michael Myers mask and that mask later became possessed by the physical personification of a cosmic force known as Evil. So when Michael put the mask on, He became the Physical Personification of Evil. He was bound to a complex set of rules and customs. One which requires him to spill the blood of his family or he is no longer protected as the personification of Evil from other Personifications. Another is that he can not come across the presence of a loved one or the mortal's downfall is assured. Michael also becomes mortal during one day every few years. It's also fun to note The Silver Shamrock Witch Mask on the cover of Halloween III: Season of the Witch appears in the Halloween (2018) trailer