MRay is so omnipresent right now I usually run this Refrigerate MMX set with e-speed :
-2 252 Atk Life Orb Refrigerate Mega Mewtwo X Extreme Speed vs. 4 HP / 0 Def Rayquaza: 395-468 (112.2 - 132.9%) -- guaranteed OHKO
Yeah even after a POSSIBLE King's shield, the MRAY is killed. So well, you...