Pokemon Diamond Discussion
Grass Knot, Focus Blast/ Aura Sphere, Ice Beam and maybe Calm Mind with a Life Orb would be pretty effective in Ubers.
Though most people who aren't competitive will likely be sweeped with a Psychic/ Aura Sphere/ Ice Beam combo.
Thunder should be used if you also have a Kyogre on your team.
Most people who are not competitive will lose to a Kyogre with a Choice Scarf using Water Spout.
If you want a competitive Mewtwo take a look at Link.
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