I had this idea for a Zombie apocalypse scenario pop into my head. What do you think of it?
>Plot of XY, but Lysandre uses both Xerneas and Yveltal to power the Ultimate Weapon
>His plan succeeds, the Ultimate Weapon fires, causing countless deaths.
>But something goes awfully wrong.
>Those who were presumably killed walk the earth again. But they've changed.
>They're rambling corpses, not alive, but not dead either.
>Devoid of any emotions, desires, personalities, whatever made the former being special.
>What's left is an unnatural urge to devour and destroy.
>Having tampered with life and death, Lysandre gave rise to something abominable, now threatening all life on earth.
>It spreads like a disease, infecting more humans and pokemon on its way.
>Not long, and Kalos falls. Next Palea and Galar, and after that the entire globe.
>There's no protection from it, anything that comes close to those abominations turns sooner or later.
>Not infected, more like corrupted.
>Only a few are immune to it.
>Notably Zygarde, which - for whatever reason - is targeted by the disease.
>Possibly a natural threat to the blight, capable of restoring order.
>Despite this, Zygarde struggles, with the disease becomes stronger with each passing day.
On a meta level, you could interpret it as the zombie sickness being some sort of cancer (explaining their uncontrollable spread, unsatiable hunger and meaningless destruction) and Zygarde representing a healthy organism fighting against it. Also, it's less a pathogen and more the life essence of living beings becoming corrupted, since XY is all about the life energy of pokemon.