Yveltal @ Life Orb
EVs: 32 Atk / 252 SpA / 224 Spe
- Dark Pulse
- Sucker Punch
- Oblivion Wing
- Focus Blast / Roost
Dark Aura is a great Ability. It increases Dark Pulse's Base Power from an iffy base 80 to a much more impressive 106, and slightly more. Yveltal may not have the best Sp. Attack for a BST 680 Uber, but having a main STAB Attack that would make a Special Earthquake look bad certainly helps.
However, one of Yveltal's mains strengths by far is its Sucker Punch. This time, I like to think of Dark Aura as a Boost to Attack as apposed to Base Power. So, with the given Attack EVs, Yveltal has just 306 Attack, but with Dark Aura, Yveltal has the equivalent of a much more impressive 408 Attack. And with an 80 BP STAB, with the boost of a Life Orb, Yveltal's Sucker Punch is one of the strongest priority moves in the game, and you honestly will be losing out if you choose not to run it. It also greatly lessens the overall need to be fast and quite simply makes Yveltal much more useful.
Speaking of Speed, the given EVs let Yveltal outrun Pokemon with a Base Speed of 95 or lower with a neutral Nature. You can run Hasty over Mild if you really want, but due to Yveltal's odd base speed there's virtually no reason whatsoever to increase the speed EVs. As a Mixed Attacker, a Defense lowering Nature is preferred over SpD, due to the fact that Yveltal's typing is slightly better at switching in to Special attacks (it also loses slightly fewer points).
Next, Oblivion Wing acts as secondary STAB and covers Fighting Types. IMO Oblivion Wing is simply better than Hurricane. his is because of two reasons: 1) Outside of Rain, Hurricane is weaker on average, at 77 Base Power, not to mention that its accuracy will annoy you to hell and back 2) Oblivion Wing also has a vastly superior side effect that greatly improves its tanking Ability. Whenever something outspeeds it, that it cannot OHKO outright, Yveltal can use Oblivion Wing to greatly minimize the overall damage and then potentially follow up with Sucker Punch to achieve the KO.
For this very reason Dark Pulse already is not always the best move to use, even though it's much more powerful, and Hurricane is pretty comparable to Dark Pulse in that regard. Even with Rain support, Hurricane is still very questionable over Oblivion wing. Focus Blast is a bit of a luxury move; while there are a handful of things that Yveltal needs Focus Blast for, coverage-wise, it also tends to be useful for its ability to simply hit things Super Effectively. It's nice to quickly remove the Normal, Steel, and Dark Types and make the game just a little bit easier.
Of course, you cannot be blamed for running Roost Instead, though Oblivion Wing helps for recovery.