QC APPROVED 1/3
Grass Knot OHKOes Groudon at +0, Ice Beam fails, good enough to mention in AC. A stronger hit on Ground Arceus, Tyranitar, and hits most Kyogre harder than Psytrike.
I think a mention of Lugia and Giratina being more annoying for the bulky attacker than then main Calm Mind set is needed. Both can now easily survive even +2 Ice Beam and phaze you or status. The lack of Life Orb and investment in Special Attack is pretty huge in the damage output against those walls.
In counters section, Bisharp should be added as a check. Sucker Punch OHKOes all the time, and we already uploaded Bisharp on site for quite some time now. Night Slash can crush Mewtwo as well so there will be some mind games. Aura Spere or Fire Blast destroys Bisharp sadly. If the stalltwo set drops Will-O-Wisp for Toxic, Bisharp walks all over you and pretty much any Steel-type with decent offenses such as Scizor.
Sucks, but Heracross deserves mention as one of the few things who can OHKO any Mewtwo set with Megahorn. It also doesn't mind a burn as much as Genesect would. Approving Scarf set too, it has insane Speed to revenge kill weather abusers and Rock Polish Groudon. You can also survive one Stone Edge from Rock Polish Terrakion and OHKO it back.
Nothing else to change, this is a good but huge analysis.