Patent attributes
A gaming machine may determine that a trigger event for a bonus game occurred during a base outcome event of a base game, wherein the base game and the bonus game are both reel-based games being executed on behalf of a client machine. In response, the gaming machine may award use of two or more replaceable symbols for the bonus game. Until all of the replaceable symbols have been used, the gaming machine may repeatedly carry out iterations of bonus game operations including: determining a symbol set for display on a plurality of reels, where the symbol set includes non-replaceable symbols and zero or more replaceable symbols, and where each displayed replaceable symbol is successively replaced in the display by either a new non-replaceable symbol or a new replaceable symbol until no displayed replaceable symbols remain on the plurality of reels.