Some methods involve receiving user input for initiation of an instance of a slot game, determining a game outcome that includes corresponding display symbols and an award determination, controlling a display system to display the display symbols at a plurality of display symbol positions and controlling the display system to present award effects corresponding to the award determination. The display symbol positions may be arranged in display symbol rows and display symbol columns. At least one of the display symbols may be a metamorphic display symbol that includes a metamorphic image. A state of the first metamorphic image may correspond to a level of progress towards attaining a goal. Progress towards the goal may be based, at least in part, in the number of occurrences of the metamorphic display symbol.