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I have bee looking for such an Yveltal for quite a while to join my Modest GeoXern (I also have a Timid Xerneas but in my experience GeoXern doesn't need a +Spe nature) and my shinies are just going to collect dust, so I'm not arsed about trading two for something I really want.
I am going to get an egg from the Absol for Justified and Baton Pass, so it will be ~L10 when you get it. It's [original] moveset will be Baton Pass/Megahorn/Play Rough/Zen Headbutt.
After much some deliberation, I figure the Yveltal is close enough for me not to be miserly about my initial offer. I'll take it for any two shinies I am offering, or one & a not-Ability Capsule BP item.
I also have a shiny Frogadier I just caught in FS (L30, Quirky, Torrent, x/31/x/x/31/x) and I'm in line to get shiny Noibat & Skiddo, if you're willing to wait for information on them.