A gaming machine. A memory stores a first set of symbols including first, second, and third symbols, and a second set of replacement symbols. A symbol selector selects symbols from the set of symbols, displays the selected symbols, and selects a replacement symbol to replace a selected third symbol in response to the third symbol being selected. A value assigner randomly assigns a prize value to a selected first symbol. An outcome evaluator determines if the selected symbols include a defined number of first symbols, and triggers a feature game when a defined number of first symbols are selected. Until an end condition is met in the feature game, the symbol selector causes the display to retain a selected first symbol, remove a selected second symbol, and replace the removed second symbol with a symbol selected from the feature game set of symbols.