What Pokemon is Psychic hitting that Psystrike doesn't already KO just as fast? Timid Psystrike 2HKO's Primal-Groudon after stealth rocks, as does Psychic. I suggest running Ice Beam, which OHKO's Zygarde and Yveltal after rocks.
252 SpA Life Orb Mewtwo Ice Beam vs. 132 HP / 0- SpD Yveltal...