name: Psycho Killer
move 1: Psystrike
move 2: Ice Beam
move 3: Fire Blast/Calm Mind
move 4: Aura Sphere/Recover/Taunt
My version of the extremekiller.
If you want to put holes in people, you want four attacking moves. If you want to attempt some sort of (mini)sweep, you should use better coverage moves. With stealth rock on the field, the vast majority of things are OHKOed by psystrike, ice beam, or aura sphere. Calm Mind and fire blast doesn't do very much for coverage, your sweep will be stopped by ttar or dialga. The only common pokemon to take the three coverage moves I suggest is forretress, who still takes like 70% from aura sphere. Recover could be used to preserve mewtwo. It is a very dangerous pokemon and if preserved can stick around to inflict more damage. Taunt would be used primarily if mewtwo was used as a lead, to prevent hazards.
Bottom line: If you want to attack right away you use fire blast. If you want to set up and sweep you use calm mind. Taunt and recover are other niche options, and could even be put in AC or OO, or whatever section they belong in.