Mewtwo

Your team will certainly be a good one. Now, will your partners use crap or not is the question.

You might also want to figure out what to do if the Mewtwo has Focus Blast. Better to have a plan then throw something together on the fly when you find that the recommended list doesn't have your Ttars on it, implying Focus Blast.

Double dark gyarados reaches a breakpoint with bite at lvl 31 with a 15 attack iv. Doesn’t look like the 2776 Gary has reached that yet. Also, if the mewtwo has confusion then Gengar might not last long enough to be viable. You might want to switch it out with a DT/O Dragonite, which performs similarly (and some times better) to a double dark Gary.

Put the B/C ttars in the FB team. They will die fast but you will get 2-3 crunches from each. Prepare a party for FB B team with the Gary and dragons so you can rejoin quickly with a good team. If M2 has confusion don't put the gengar first since he will eat 2 consecutive confusions.
If you have houndooms they will do better than the Gary in non FB.