Buzz's BB gun first appeared in Home Alone. When the McCallisters left Kevin home alone, he took Buzz's gun and practiced shooting it on some Sports figures. When Harry and Marv broke into his house, Kevin used it as the first booby trap, shooting Harry in the groin and Marv in the forehead, causing both men a great deal of pain and distress which only fueled their motive to harm him.
Kevin using the BB gun