In the official Pokedex, it says that Lugia does not have gender. In many games, there is only one Lugia.
But in EP221 a Lugia's pup is shown and captured by the Rocket team, and Lugia, hitherto genderless, is treated as "the mother who fights for her son."
If Lugia is a legendary and genderless type and, possibly, unique, how can he have a puppy? Legendary can reproduce even if they have no gender?