My 2nd EX raid
Valor gym. The same players as the ones who controlled the gym at my first EX raid.
6-man private group. Took down Mewtwo in 3 minutes/180 seconds. 11 balls. Mewtwo CP 2237.
I also helped my entire group organise their battle parties. Apparently one of my level 40 teammates maxed out a 100% Pinsir with Vice Grip, without even knowing it was literally the worst move in the game. I TMed it to X-Scissor for him.
My battle team is in the screenshot below:
Catching Mewtwo:
For the first 4 balls, I used pinaps, as it was lower CP than my first one. Broke free even with great/excellent curves. Wasted 2 balls with attacks.
Last 6 balls, all GRB. 3 great, 2 excellent, 1 nice. It still ran away.
I don’t really care since I already have a Mewtwo. But just for everyone to know:
Don’t overestimate Mewtwo’s catch rate.

Answers
Gengar is very squishy, but outputs amazing DPS if you have one powered up with Shadow Claw/Shadow Ball. Against Mewtwo with Psycho Cut/Focus Blast, it's amazing.
The only time when Gengar isn't so optimal is against Confusion/Shadow Ball Mewtwo, as it will likely faint to the dodge glitch after Mewtwo uses its first charge move (in my experience anyways)
Today we were 5. A guy from the local group, a guy with his and his girlfriend's phone an older funny lady and me.
However, I saw some Aggrons in there an Alkazam, Lugia and some other questionable picks The 2and round was auto selected (no one made the effort to prepare a team before) and we still did it. (Mewtwo had SB)
It was close but not the "OMG, will we do it?"-close
Everyone catched it which is most important. For the Lady it was the first one. Mine was 2239 (thats the one with 15/15 but only 10 attack) which I already had so I pinaped him.
Team was
3670 Ttar B/SE
3653 Ttar B/C
3645 Ttar B/C
3138 Ttar B/SE
2621 Scizor 2xbug
2168 Houndoom 2xdark
2and round some autoselect Aggrons