I don't think sucker punch would be the best because that gives the opponent the opportunity endlessly switch to pp stall me out.Oh look, yet another SwagFag set. How quaint. Just kidding, it looks fun. However, I believe that Sucker Punch would assist in KO'ing important walls, most notably the ever more present. Lugia, Giratina and the Pink Blobs *shudder*. This would entail a few changes in the EV's, but I feel would also massively increase the usefulness of the set. I think breaking Lugia and the Pink Blobs *shudder again* would offer much more to any team, and I feel would work quite well in tandem with Xerneas. Cool set, props.
I tested out max hp and it works really nice, thank you. Leftovers also works better but it was hilarious seeing the confusion of the enemy when their 100% moves missed. The reason why this set works is because of yveltal's bulk letting it take multiple of those non confused hits. Anyway thanks for the suggestions blue jay I'll make changes to the post.Taunt makes any of those walls a non-issue. I'm not even sure what makes you suggest Sucker Punch, a move that fails unless the opponent attacks you (which some walls don't even carry moves for) over Dark Pulse, which is more reliable and requires no mixed EVs.
Please don't split defensive EVs like that. Maximize HP and then pick a defensive stat to invest in, this will give you better overall bulk.
I'm also really not sure about the set. Swagger etc is nice if you get lucky. IF. Meanwhile, you're sacrificing valuable and reliable coverage for it. Brightpowder is also too unreliable to truly be better than leftovers on a set like this.