This article presents observations and strategies for designing game-like elements for expressive mobile musical interactions. The designs of several popular commercial mobile music instruments are discussed and compared, along with the different ways they integrate musical information and game-like elements. In particular, issues of designing goals, rules, and interactions are balanced with articulating expressiveness. These experiences aim to invite and engage users with game design while maintaining and encouraging open-ended musical expression and exploration. A set of observations is derived, leading to a broader design motivation and philosophy.