>>18367805Legendary pokemon are a special exception. In the cases where it's the only one in existence (in Pokemon canon), it's generally referred to by a gender, such as Arceus being male, Meloetta being female, Mewtwo being male, etc.
>>18367859Genderless pokemon, like others said, are generally artificial; either that, or they're like snails, and are all just one gender.
How the artificial pokemon reproduce is beyond me, but who cares.
