A gaming system includes a gaming machine, a random element generator, and game-logic circuitry. An initial outcome is displayed in the form of a plurality of symbols arranged in a primary array and a secondary array, the primary array including a plurality of primary reels and the secondary array including a secondary reel. In response to the plurality of symbols including a trigger symbol, one of the primary reels is substituted with the secondary reel to form a modified primary array. A modified outcome is determined based on the modified primary array.