I'd keep the Gardevoir with C/DG, possibly change the Tyranitar to crunch but it would depend on if you have enough other rock attackers (Golems). All indicators point to Moltres, Zapdos, and Articuno returning. Even if you don't have those good rock attackers, your Tyranitar would do somewhat better with crunch. Dragon attacks are fine vs. Mewtwo, use them if you don't find a lot of Houndooms/Scizors/shB Gengar, etc
Gardevoir TM Question
I have my first EX Raid on Friday, and I don't have all the perfect TTar counters. My highest is a 2762 TTar whom I'll power up to level 30. Other than that, I don't have the greatest of counters. I do have a level 30 perfect Dragonite, a level 29 Rayquaza which I'll also be powering up to 30. Level 30 Raikou, and a few other high DPS but not SE counters.
I do have a Gardevoir which is level 35 and perfect. Right now it has Confusion/Dazzling Gleam. Should I temporarily TM it to Charge Beam/Shadow Ball?
I also have a high level Alakazam with PC/FS. Should I TM that to Shadow Ball? Please advise!
Edit: My best TTar has Stone Edge right now. Worth TMing to Crunch?
Answers
Don't sweat Mewtwo too much. The battle isn't actually that difficult so, assuming you're not doing it with limited numbers or deliberately trying to low-man it, any half-decent mons will be able to take it down with relative ease, even if they're only doing neutral damage.
As such, I wouldn't bother to TM any of your mons as it think it will be unnecessary, unless perhaps you're swimming in them. Your Tyranitar will be your best option, and although Crunch is the best charge move for this application, it will still do a ton of damage even with Stone Edge.- Bite is the move of importance.
I've counted 8 or 9 people that I could find are coming. They are of different teams, but if we can't find enough to split, I'm assuming everyone will go in together. I do try and throw excellent curves, so hopefully 7/8 balls should give me the Mewtwo. I've seen enough videos to know Mewtwo will be easy with 8/9.
I use a fast TM all the time just to change a move for one battle. But their behavior is simple and predictable. It is easy to go back. With a charge TM, it is an entirely different situation. It is quite possible you may have to use a lot of them to get the move you want, and then again to change back. So I would not use a Charge TM to get a better move "temporarily". Mewtwo is not a difficult fight with enough people, save your Charge TMs.
It depends on your tm situation. If your best counter is a level 30 Tyranitar with B/SE, then a CB/SB Gardevoir will be an excellent choice. However, I wouldn't use a charge tm unless you have LOTS. If you have a handful of fast tms, I'd use one since charge beam is better than confusion against Mewtwo.
As others have said, just bring your best team and you'll probably be fine. A perfect, level 35 Gardevoir with any moves (except Psychic) will be fine against Mewtwo with a big enough group. Any weather boosted legendary with any moves will be a decent choice as well. Basically, go down the list of decent counters and pick the best mons you have. You should be fine.