Honestly, a Mewtwo lacking Psystrike is not really worth running it imo. Might be a good place for your ETM
The niches per pick:
- Shadow Ball does great damage against Giratina’s and Metagross, decent neutral damage on meta pokemon. Energy req is 55
- Flamethrower does great damage against steels. If not running Shadow Ball, then this is necessary to not get walled by Steel-types. Energy req is 55.
- Ice Beam OHKO’s Dragonite and does neutral damage against almost non-existent Tyranitars. Energy req 55
- Thunderbolt does great damage against Kyogre and neutral damage against Steel-types. Energy req 55
- Focus Blast OHKO’s steel-types and Rhyperior if Mewtwo manages to land this. Energy req 75
- Psystrike hits INCREDIBLE (90 damage for 45 energy) on almost everything, and even deals 1/3 damage to Dialga/Melmetal that resist it.
Now, I’ve put the energy req with each move too. This is because you’ll have to know that Psycho Cut - the fast move - does little damage and can rarely be relied on to knock an opponent out. So you can count on it that in 90% of your matches, Mewtwo needs 2 charge moves to KO an opponent.
So if you need 2 charge moves - why not use Psystrike at 45 energy, instead of Shadow Ball at 55 energy? Ice Beam is great for Dragonite, but can’t be relied on if shields are up. Dragonite is likely to win if there are shields in play, and you can’t pull off 3 charge moves if lacking Psystrike (this is the same case with Dialga, Togekiss, Snorlax and Kyogre, too). Unshielded, Psystrike hits so hard, but you’ve probably seen this on your other Mewtwo too.
In that perspective, Psystrike is pretty much mandatory to get the most optimal performance out of Mewtwo. And to not get walled by steels, anything but Ice Beam is viable. Actually, any movesets where you need 2 charge moves - regardless of SE factor or not - the 2nd charge move besides Psystrike is not even necessary. It’s just Flamethrower and Shadow Ball remaining really to deal decent damage to Steel-types - and Shadow Ball has the better DPE of the 2.
An example; do you really need Thunderbolt to hit Kyogre harder, if you’ll need to finish it off with a 2nd charge move anyway, whereas 2 Psystrikes would also KO it?
Do you really need Shadow Ball to hit Giratina harder, if you’ll need to finish it off with a 2nd charge move anyway, whereas 2 Psystrikes would also KO it?
I know Gamepress rates this moveset high, but honestly I have not seen a single Mewtwo lacking Psystrike so far and they are definitely making the right choice. I love using it, hate getting Psystriked my own ass