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>When Zygarde used up its strength protecting pokemon from the light of the ultimate weapon...
>its parts scattered to far-off places, absorbing the power of those lands and seeking humans who would give it aid.
>And now that I think of it...
>The moves that Zygarde used when it Mega Evolved-they reminded me of Z-Moves, like those used in the Alola region.
>...But perhaps I am reading too much into it.
So did Necrozma teach him how to make his own Light That Burns The Sky with Nihil Light?
This also explains why he was in Alola.