Mewtwo Team?

That team isn't bad, but it could be better with more TTars. Gyarados and Dragonite aren't really preferred unless Mewtwo knows Focus Blast.

Movesets and potential alternatives that you decided not to bring would be helpful.

I'd get rid of the Snorlax though regardless of moveset. You want to get in as much damage as possible in as little time as possible and Snorlax just doesn't output damage fast enough.

It doesn't matter if your entire party faints because you can just rejoin since damage bonus is retained, but in the time it takes for a Snorlax to faint you could have gone through 2 Pokemon that would have done more DPS and potentially earned you more damage bonus balls.

Consider making multiple teams for different movesets. Focus Blast destroys Tyranitar and Snorlax, and Psycho Cut can open the door for Gengar and Houndoom.

The Tyranitars are great, but too many non-STAB attackers. If you have them, use Snarl/Foul Play Houndoom, Fury Cutter/X-Scissor Scizor or Bug Bite/X-Scissor Pinsir.

You want double ghost Gengars in there for high DPS, even if the Mewtwo has confusion. Gengar gets knocked out quickly, but he does his job while he’s in there. Your T-tars are good, just be ready to dodge focus blast if that is the Mewtwo’s charge move (you’ll know if the T-tars are not autoselected). Bugs are good if they are level 30 or so. And shadow ball Alakazam if you have one. Dragonite’s can fill in if you don’t have anything better. But T-tars and Gengars are the real heroes against Mewtwo.