You will just have Shelly as your brawlerwhen you start out. You will have to open boxes to unlock extra brawlers. These expense 100 coins or 10 gems to open. You will not constantly get a new brawlerwhen you open a box. Do not stress. The other possible rewards from boxes are just as helpful. You can get Elixirs which can be used to upgrade existing brawlers. If the box consists of a brawler that you currently have, you will also get Chips. Chips can be used to unlock rarer fighters!