Ranks for each minigame range from one to five stars and are displayed on the player's in-game profile. The criteria for these ranks are intentionally kept secret, but ranks always increase with each play. Each rank up requires more effort than the last, but will also reward you more gems. Achieving a five-star rank unlocks a unique badge and a Steam achievement for that minigame.
Reach a five star rank in all minigames to unlock the Expert badge.