>>18352726Psystrike is an auto-include for Mewtwo. The only reasons not to run Psystrike on Mewtwo are if it's underleveled and thus hasn't learned it yet, in which case why are you even playing against other people, or you're literally retarded.
Psystrike/Ice Beam/Aura Sphere/Shadow Ball is THE offensive set for Mewtwo. Perfect coverage and a STAB that can OHKO or 2HKO pretty much everything that doesn't resist it.