TL;DR: You need a lot of coverage, with baton passers to back mewtwo up.
Mewtwo with mewtwo x stone.
Evs: 252 Attack, 252 Speed, 4 Special Defense
Mewtwo with mewtwo y stone
Evs: 252 Special Attack, 252 Speed, 4 Defense
Grass Knot for Arceus, MRayquaza, PGroudon, and PKyogre.
Mewtwo X only has one Pokemon who is Immune to all his attacks, shedinja, none that are hit not very effective by all, 235 hit normal by all attacks, and 564 that are hit super effective by at least one, some being the all powerful dragon types and things like mega garchomp and tyranitar.
Mewtwo Y also has one immune, but 3 not very effective, the magnemite line, 344 neutral, and 452 super effective.
An assault Vest could also work, but I recommend mega stones.
I have also found this set works well with two baton passers before it, Drifblim and Scolipede. Drifblim has this set
Bright Powder/Sitrus Berry/ Mental Herb
Evs: 252 Hp, 252 Speed, 4 Special Defense
Substitute / Destiny Bond
This helps because the Evs for mewtwo go into attack/special attack and speed, not defense.
252 Speed, 252 Hp, 4 Defense
Substitute / Protect
Agility / Iron Defense
This will help mewtwo sweep.
If you use mewtwo y, Scolipede will not work.
You need ambipom.
252 Speed, 128 Special Defense, 128 Defense
Hone Claws for accuracy or Substitute for protection.
The hone claws can be very helpful because blizzard and thunder have low accuracy.
Both Scolipede and ambipom need timid or Jolly nature.
You could also go with fire Punch on mewtwo x for shedinja, but I don't recommend it.
Focus Blast on mewtwo y instead of grass knot could work, but it depends.
After all this, Mewtwo only has a 1/3 chance of being hit by attacks, and can wall them out while still sweeping like a pro.
Hope I helped :3