Considering Yveltal is the only Pokemon yet that can absorb 105% of the damage dealt with Oblivion Wing [Big Root], I'm going to give it to the only Dark Type legendary Pokemon. I never really used Xerneas much to actually have an opinion, and Zygarde? Dime a dozen, those Dragons. Yveltal's Oblivion Wing reminds me of Tactics Ogre's Drain Heart: "Heartbeat of life, gossamer wings, return to roost, to me!" pretty fitting, no?