Harshal Karvande, Game Design Lead at Rovio, deconstructs the hit mobile game’s season pass and XP system — Battle Legion is a F2P strategy game, developed and published by Traplight, where players collect, upgrade and customize a deck of army units that engage in quick, auto-play, bite-sized battles. Players earn XP after each victorious battle, which advances them on the fortnightly season pass. Players also have a reserve…