New Super Mario Bros. 2 has more gold coins in it than the United States Bullion Depository and the Federal Reserve Bank of New York combined, but the only way to extract real, honest, actually completely fake gold from the game is to pre-order it from either GAME or Gamestation in the UK.
The "gold" coin seen above is actually a small case for storing a single 3DS cartridge and is only available as a pre-order bonus from the aforementioned English retailers. By being so pretty and yet so impractical, the coin case satisfies the two most important bling requirements: Flashiness, and superfluousness.