Mewtwo ready?
With these 5 battle parties, am I ready to fight Mewtwo on Christmas? At least 6 people confirmed on Facebook that they are going, though there could be more (spoofers)
PC, not FB:
1: Gengar L31 SC/ShB 12/11/14 82%
2: Ttar L30 B/Cr 15/14/11 89%
3: Ttar L28 B/Cr 14/15/14 96%
4: Ttar L30 B/SE 15/14/12 91%
5: Ttar L32 B/FB 14/09/15 82%
6: Snorlax L29 L/HB
PC/FB:
1: Gengar L31 SC/ShB 12/11/14 82%
2: Ttar L30 B/Cr 15/14/11 89%
3: Ttar L28 B/Cr 14/15/14 96%
4: Gary L34.5 B/Cr 15/15/13 96%
5: Dnite L31 DT/O 14/14/15 96%
6: Dnite L30.5 DT/O 14/15/13 93%
Confusion, not FB:
1: Ttar L30 B/Cr 15/14/11 89%
2: Ttar L28 B/Cr 14/15/14 96%
3: Ttar L30 B/SE 15/14/12 91%
4: Ttar L32 B/FB 14/09/15 82%
5: Ttar L25 B/Cr (weather-boosted raid catch, mediocre IVs)
6: Gary L34.5 B/Cr 15/15/13 96%
C/FB:
1: Ttar L30 B/SE 15/14/12 91%
2: Ttar L30 B/Cr 15/14/11 89%
3: Ttar L28 B/Cr 14/15/14 96%
4: Gary L34.5 B/Cr 15/15/13 96%
5: Dnite L31 DT/O 14/14/15 96%
6: Dnite L30.5 DT/O 14/15/13 93%
Rejoin team (Only for C/FB and maybe PC/FB):
1: Banette L28 SC/ShB
2: Ttar L25 B/Cr
3: Gary L30 B/Cr 13/15/13 91%
4: Alakazam L30 PC/SB 13/13/12 84%
5: Dnite L30 DB/DC 10/15/10 77%
Answers
You likely won't know the moveset ahead of time, so you'll need to come up with a compromise team, although the autoselect telegraphs focus blast by ignoring your Tyranitars.
Like you, I obsessed over my Mewtwo team, but the reality is that it probably won't matter much. If it is a relatively small group (6-8), maybe you can get one extra ball by optimizing your team.
Do you have any high-level double-bug Scizors or Pinsirs? S/FP Houndoom is also good. And against focus blast, use up to three double ghost Gengars if you have them.
But you'll probably be fine.