Certain examples disclose a gaming system comprising a display, a symbol selector, a symbol evaluator and a symbol modifier. The example symbol selector is arranged to select a plurality of sets of symbols for display on the display. The example symbol evaluator is arranged to determine whether the displayed symbols include any winning symbol combination. The example symbol modifier is arranged to, upon a determination that the displayed symbols include any winning symbol combination, repeatedly apply a modification rule to at least one of the plurality of sets of symbols until the displayed symbols do not include any winning symbol combination.