Talk:Darkrai/@comment-38578289-20190709054653/@comment-38578289-20190912062718

No, heatran is alone. Bulbapedia clearly states that they both form the lunar duo. They are hostile toward each other, because the psychic type from gen 2 - 5 was the counterpart type to the dark type, as the fairy type did not exist until gen 6.

More about the lunar duo can be found here