Engagement exercise
This exercise iterates on the predictive example by adding a simple rock paper scissor fighting mechanic. The game "works" but it gets old quickly. Add one or two mechanics that increase player engagement.
What hooks up to a game and what makes you come back? A sense of progress? Sense of community? Personal investment (or sunk cost fallacy)? New content? Unlockable content? Delayed reward schedules and (exploitative design patterns)[https://techcrunch.com/2010/08/25/scvngr-game-mechanics/]? Go through the Koster's (mechanics for social games)[https://www.gdcvault.com/play/1014555/Social-Mechanics-for-Social-Games] - not all of them apply of course.