You only get XP points from completing missions, so it’s a good idea to go as far as you can in the campaign in order to unlock additional content and gear. There is only one way to gain XP in Shadow Fight 3, which makes it a slow process overall. You might want to try it out right away, but you have to be level 3 to equip it. Take, for example, the gorgeous sword that drops off the first boss. Levelling up goes hand in hand with gear improvements, especially since some gear will require your character to reach a certain level before it can be equipped. As an F2P player, make sure that you don’t spend on unnecessary cards and instead focus on those cards that would increase the efficiency of your current gear. The game does give you some free coins and premium currency right off the bat, which you can use in the Shop. All you have to do is to upgrade your current gear a few times and this will drastically reduce the boss’ difficulty.
Most likely, the fight will show up as “Insane” in terms of difficulty, which can feel impossible even for the most experiences SF fighters.
