'Make stars feel like stars': Why -- and how -- Madden game designers created 'X-Factors'

Two designers at EA Sports created "X-Factors," unlockable in-game attributes that temporarily power up star players.

source https://www.espn.com/nfl/story/_/id/29710816/make-stars-feel-stars-why-madden-nfl-video-game-designers-created-x-factors