I dont think Mewtwo Psych Up works, because on this metagame with sash u are exposed to Hazzards ( Who set up without hazzards) and u are exposed to priority like Extreme Speed or Sucker Punch, the idea isn't bad and its old, to be honest there's a spread that make mewtwo survive moonblast after SR but priority its a danger and u cant only solve that problem with Tapu Lele cuz terrains can get nullified.
Yes, this Mewtwo requires hazard support. But what is gonna nullify psychic terrain in ubers? Tapu koko is the only other real tapu in Ubers and is all the way down in B, and really doesn't see a whole lot of usage. EV'ing mewtwo to live a +2 moonblast requires a 252hp/252+spd, literally the opposite of a mon that fits on an offensive team. Also, lots of modern HO sets up without getting hazards immediately; set-up-and-go offense seems pretty common on the top end of ladder. This is what my set was made for.
Anyways, it does work, I used psysash HO to ~1600 on the old ubers ladder before the reset.