My plan has remained unchanged:
- Keep raiding for candy
- Use candy to work on maxing out my 93% Shadow Ball Mewtwo (currently ~L34)
- If unable to get enough candy before the 23rd drop rare candy to cover the difference (I have over 550 RC)
- Keep highest IV Mewtwo of other charge moves
- Mark the rest for trade or transfer, depending on Halloween bonuses
The only thing I'm undecided on is what to do with my current L35 Mewtwo. It has Shadow Ball and was my first and only for several months having gotten it during the field test period but it's only 78% IV with 11a. I want to max it but 35 -> 40 is stupid expensive for little gain.
In your case I'd power up the Shadow Ball one for sure and sit on the other two for the time being, unless you need an ice attacker and a psychic attacker.