>>52264022I did a couple solo during the Scarlet pre-release.
Bring the right Pokemon(super effective move for the Tera, no super effective weaknesses), the right nature via mints, Hyper Train at least your damage dealing move, Choice Band or Specs and have your Pokemon at least level 75.
You should have the resources post game to make at least one Pokemon viable and use the rewards from 5 stars to make more. I assume 6 star is even more of a bitch and I'll just stick to online for those.