And odd. One type Yveltal's immune to, one Xerneas is immune to. So it can strive to maintain order but the cycle of life and death goes on (mostly) unchanged? Also, it seems like Xerneas and Yveltal battling can symbolically represent life and death: early on, it's clear that life is winning (because Xerneas has SE STAB) but in the long run, death has more staying power (due to the healing from Oblivion Wing) that means that, as long as Oblivion Wing heals a decent amount, the battle between life and death will go roughly as expected.
Generation (pi)(i). When you see this, raise e to the generation and add 1. Social experiment.