Well, not anything. You don't have weapons (and can't get your battle suit or Porygon -- erm, yeah, Sharpen doesn't really work that way, sorry to say, but it's fine to leave as is in that post -- to materialize one), and if you do something to another player's character or Pokémon, you've got to check with them first. That and you can't do something such as taking out an entire team by yourself in one or two shots. But other than that, the rules are pretty lax about what you can do to NPCs.