Silent Night, Deadly Night

A young boy witnesses his parents' brutal double murder on Christmas Eve by a man disguised as Santa Claus. He grows up in a dysfunctional Catholic orphanage and undergoes psychological trauma due to the cruelty of sadistic nuns, leading him toward a psychological breakdown in adulthood. His childhood trauma eventually emerges when he is coerced into playing a department store Santa, causing him to snap and unleash a killing spree on anyone who gets in his way.