Gold Block is an item that appears in New Super Mario Bros. 2 as a way into following the game's gold theme.
This item can be gotten once a Brick Block is hit ten times in a certain time limit until turned golden. Some gold bricks are found already in the gold form (without requiring to hit a brick block). Then, it can be worn by Mario and Luigi. Then, coins are obtained in a slow pace. Mario and Luigi will generate coins until they are hit or the block is destroyed after a certain amount of time. The faster Mario/Luigi runs, the faster they get coins.
If the Gold Block is hit with a Koopa shell or if Mario/Luigi already has a gold brick, then it throws coins up until it disappears after a period of time.