The Good Son (1993)

When a young boy named Mark is sent to live with his aunt and uncle after his mother's death, he quickly learns that he has a darker side. Mark's sociopathic tendencies manifest in sadistic behavior, including the killing of the family dog. As his deception and manipulation grow more elaborate, his cousin Henry becomes suspicious of his true nature. The film culminates in a deadly confrontation between the two boys, ultimately revealing the extent of Mark's evil.