Alien Beach Party Massacre

In the summer of the year 2000, a peaceful alien race called the Mirusian steals a weapon called the Deathsphere from a hostile alien race called the Ghastorian, and while attempting to transport it to a lab, their ship is shot down by the Ghastorians and they must crash land on Earth. Before they crash they shoot the weapon like a torpedo from the ship to some location on Earth. There is only one survivor of the crash, the least intelligent of the crew, who before they were attacked was using a highly advanced mop to clean the floor. He must locate the Deathsphere before the Ghastorians do. He gets confused for someone else and becomes part of a group having a beach party while the Deathsphere gets mistaken for a volleyball which some young people play with. The Maltrusian alien along with the Deathsphere go off with a group that separates from the party to go up to the mysterious abandoned house of the deceased Mr. Willoughby.