Special Attack doesn’t matter, because your Zygarde isn’t using any specially offensive moves anyways. HP and Attack are the stats most important to your tank, so you should soft reset for at least perfect IVs in HP. If you really don’t want to, you can just level up your Zygarde to 100 and use either 2 Bottle Caps on it, or 1 Gold Bottle Cap. The easiest way to find them is by saving next to a fishing spot with swirls around it, and fishing. Every time you find anything that isn’t a cap, soft reset. Also, there’s an event going on this month at GameStop where you can get a code for a level 100 shiny Zygarde holding a Gold Bottle Cap. (If you’re playing the Ultra version of Sun or Moon.) So, you could just get that Zygarde, soft reset for an Impish Nature, and use a Gold Bottle Cap on it.
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