A Set in Three Mechanics

The pendulum swings, but make no mistake, its resting state is not the center.

Every set needs to introduce new mechanics to entice players, even if it offers a new gameplay experience by remixing existing mechanics; that's [one of] the biggest reason[s] the core sets were so unpopular for so long. But how many new mechanics does a set need? 1? 3? 5+?

Kaladesh's success demonstrates 3 is one ideal.