From the Super Mario Wiki
Memory Master is a harder variation of the minigame Memory Match found in Super Mario 64 DS. While the rules are the same, matching the correct pair to clear the challenge and gain a Star, and plenty of Coins to keep playing. There are now sixteen cards upside down instead of eight, and the player bets five Coins aside three. Every time Luigi deals the cards, four of them will flip, allowing the player to have a clue to find their twins afterwards.
As the player matches the wrong pair, a Coin will be taken away from the bet amount. Losing all these Coins would remove one Star gained from the challenge. Once the player has spent all his or her money to bet, the game ends.
 In-game instructions
If Memory Match was a piece of cake for you, try out this harder version. You now have more cards to play with.