very contested gym advice

- You can feed I believe up to 10 times in a small period, and the CP replenished diminishes unless you're using Golden Razz Berries.

- Well-fed Pokemon can still be sometimes taken down if the attackers stagger the battles and beat it in three separate battles at once, but this is very difficult and unlikely. It's usually only feasible to do this in two separate battles, so feed it when it loses its first chunk of motivation to prevent this

- A highly-employed strategy is to wear down the first attacker, so make sure the first attacker is something hard-hitting like a ZH/DG Blissey, IT/CR Tyranitar, DT/DC Dragonite, or CON/DG Gardevoir

- Set up the gym to require lots of pokemon switches. Mix Pokemon that require Machamp counters like Blissey and Slaking with Pokemon that obliterate fighting-types like Gardevoir and Hex/SB Gengar

https://m.youtube.com/watch?t=82s&v=7EalNBm03r0

Get there very early. Flip the gym. Have a team of trainers with several hundred golden razz berries camp out til it hatches.

If you're in a big city it will be near impossible for then to do the stagger trick WaterYouWading4 has mentioned. There will be way too many people there to get everyone on the same page. One stray attacker should be enough to mess up the flow.

On the off chance they do remove a defender You must hold the line for ten minutes. Although the gym will be under constant attack you and your team will have a small window to drop in defenders once space becomes available. Have a berry team ready and a team of people spamming placing a defender simultaneously.

All that said its been my experience that Mewtwo is easily obtainable once you actually get the invite. More people who raid it have caught it than not. Two balls may not make a huge difference. That said if there is ever a time to really try and hold a gym its an EX raid.

Good luck.