Da Poiple Monster and his assistant, Marsha, come from Mars, see, and they... well, they strike is what they do, hence the title. We don't see them on Mars, but on Earth they have humanoid shapes, sort of (in the case of Marsha, quite a humanoid shape it is). Anyway, they have a special Martian gas that kills their victims, and they can then assume the form of their victims, which they do to advance their plot to conquer Earth (and to advance the plot of the serial). A review can be found HERE.