A new villain aligns with a familiar one in “Avatar: Fire and Ash,” the third installment in James Cameron’s franchise about the blue inhabitants of the distant earthlike moon Pandora. Arriving on the scene this time is Varang (Oona Chaplin), a passionate figure whose desire to rule is as strong as her desire to ruin. In this scene, she has cornered Quaritch (Stephen Lang), the villain from the first film, and given him a psychedelic truth serum. It leads to a potential partnership that could