Gold Mario

Gold Mario and Silver Luigi are forms debuting in New Super Mario Bros. 2, acquired by grabbing a Gold Flower. In this form, Mario can shoot big Gold Fireballs and Luigi can shoot big silver fireballs, defeating any enemy or breaking any block that is within a certain distance or any that they touch, turning them into coins. In addition, the shockwave will also empty out several non-brick blocks/brick blocks that are secretly containers. In this form, the character becomes a glowing statue made of pure gold. In Luigi's case, he becomes a glowing statue made of pure silver. In both cases, the form resembles Mario's metal form as well as the brothers' ice form from Super Mario Galaxy. If Mario/Luigi reaches the Flagpole in this form, he'll receive a coin bonus. The higher the pole is grabbed, the more coins he'll receive. Gold Mario/Silver Luigi will revert into Fire Mario/Luigi upon clearing a stage, making it impossible to keep this power-up between levels.

Trivia

 * In the first Animal Crossing game, there are two furniture items based off of Mario and Luigi, the Mario Statue and the Luigi Statue. Interestingly, the Mario Statue is golden, and the Luigi Statue is silver.
 * In Mario Golf, one of Metal Mario's palette swaps resembles Gold Mario.
 * The sprite for the gold/silver fireballs always spins clockwise, even when thrown to the left.
 * Silver Luigi resembles Metal Luigi.