TBH I think it'd be a pretty good idea to run at least ONE physical and special move each on both Xerneas and Yveltal if you're using them for an ingame run. In Yveltal's case, you have the obligatory Dark Pulse and Oblivion Wing, and then you can add Acrobatics (or even Fly) on top of that for strong physical coverage and like a coverage move like Focus Blast, or even Fly. I don't have Yveltal, but I watched a few of my friends with it and
A rank at least seems pretty justifiable. Oblivion Wing's healing factor has to be a big help on its survivability factor, right?
Since Yveltal was brought up, I'll do a writeup on Xerneas I suppose:
Xerneas: A Rank
Availability: Late, coming after the 7th gym.
Typing: Fairy, which is good defensively and even better offensively.
Stats: Same as Yveltal, phenomenal HP and offenses with good everything else.
Movepool: Only notable moves it comes with are Moonblast and Megahorn (Geomancy is usually not worth it since so few trainers in the game actually have more than 3 Pokemon, though it IS good for Lysandre and the E4), and it gets Night Slash and Horn Leech via levelup not long after. Focus Blast, Thunderbolt, Rock Slide, Psychic/Psyshock, Flash Cannon, and Grass Knot make for decent coverage moves as well. If you want, its SpA is high enough to use the Heart Scale move Aurora Beam to decent effect against anything 4x weak to it, but as most of these are Dragons you probably needn't bother.
Major Battles:
- Lysandre: Solos him easily after setting up with Geomancy, which isn't difficult.
- Wulfric: Moonblast takes a large chunk out of everyone, though there is also Megahorn for Abomasnow, Focus Blast for Avalugg, and Rock Slide for Cryogonal.
- Malva: Struggles a bit on offense if you don't pack coverage moves. Rock Slide handles all of them admirably, and only Talonflame really threatens to do much damage.
- Wikstrom: Avoid. Moves like Tbolt and Focus Blast could power through him, but it's rather risky and not recommended.
- Drasna: Moonblast wrecks her, though watch out for Dragalge (Psyshock can handle it if you have that).
- Siebold: A combination of Tbolt and Horn Leech/Grass Knot pretty much destroys everything he has, and particularly threatens you (unless Barbaracle has Poison Jab, which it may; I'm not sure, I didn't give it the chance LOL).
- Diantha: Solos her easily after setting up with Geomancy, otherwise, only Gardevoir really threatens you. Moonblast for Hawlucha, Tyrantrum, Gourgeist and Goodra, Focus Blast or Horn Leech for Aurorus, and any strong physical moves you have (or just spam Moonblast) for Gardevoir.
Other: Fairy-typing is great for most of the late-game, since there are very few opponents (bar Wikstrom) that threaten it with supereffective moves, and STAB Moonblast when boosted by Fairy Aura is enough to let you power through most things in the Elite four alone on its own. On top of that, it gets enough great coverage moves that it can afford a slot for Geomancy, which as stated is only really useful for Diantha.