Zapdos can learn the move Defog through DPPt's HM05. If you want to get it to X & Y, you must get a Zapdos from either Gen 3 (and transfer it via Pal Park) or roaming Sinnoh in Platinum and transfer it to HeartGold or SoulSilver, due to not being able to transfer Pokemon knowing HMs. Since Defog doesn't count as an HM in HGSS, you can then transfer Zapdos to Gen5. Then, use PokeBank to transfer it to X & Y.
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