If you could give a legendary a gender...

[juspate]

mew 2 struck me as male whilst mew struck as a female.
why? well voice and colour and fighting styles.

 

[King Gumball]

I always think of Uxie and Mesprit as females and Azelf as a male, although in PMD iirc Uzie was a boy... Buuutt I view Shaymin as a female, as with Meloetta (don't see why they made her genderless...). But other than Meloetta I usually don't mind legendaries being genderless. I was a little confused why they gave Heatran genders though. Kinda random and unneeded.

That Yina nd Yang and Wuji logic was interesting too! I ddin't know that ;)

 

[Mew~]

I would probably make Mew a female and Mewtwo a male.