Nobody knows how frequent they will be. Some people already have more than one, most don’t have any yet. The one you have has a very good IV spread, so I would power it up if I was in your shoes. You can’t put it in gyms, so there is no show off factor for having a better one and performance can’t get much better. Chances are your next one will have worse IVs.
GamePress
Powering up Mewtwo?
I have caught yesterday my first Mewtwo : Confusion/ShadowBall. Att 14 Def 15 HP 10 (87%). It was the first raid in my region.
Should I power it up immediately? To level 30? To level 37.5?
On the first hand, it would be an immediate contributor to my attacking lines:
- as my best generalist
- to solo Machamps
- for future MewTwo raids.
On the other hand, I only have 3 MewTwo candies, 241 rare candies, and chances to find a better IV MewTwo in the near future. If I find another MewTwo with let's say 93% IV, I would prefer to power up that one even if it has a worst moveset as I have enough TM. Stardust is not the limiting factor (rare candies are).
How frequent are MewTwo raids? How long will they last?