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Well I'd say larvesta in a premier ball and rotom with hp ice but guessing that would be too much so just larvesta(unless it isn't too much anyway) also with cobalion it can be anywhere from 0 to 30 if you really want just have to find a time/date that yields it. Either way going to hopefully successfully rng it tomorrow.
What ever is easier for you idc. But 2:1 is fine. BTW do you want Timid or Modest Rotom? Also which nature for Larvesta? I need to update my thread as it seems Volcarona's prefer Timid now a days.