From the Super Mario Wiki
Luigi's Thrilling Cards is a Table minigame in New Super Mario Bros. that is played the same way as Texas Hold'em Poker (but without the community cards). As it requires at least two human players, it is only playable in versus mode. Each player is dealt one card, but the player cannot see their card. Instead, the player sees the cards of all the other players. Without knowing what his or her card is, the player must bet on whether their card is higher than the other cards. The player that is selected to start can bet up to five coins, and each of the other players can either raise up to five coins, call the original bet, or fold. The player whose card is highest wins all the coins in the pot. Each player must bet at least one coin. If they want to bet more, they can tap Raise. If they are done betting, they can tap Next. Once they bet five coins, they cannot bet more. The next players gets to Raise, Call, or Fold. If they Fold, they cannot win and they will not have to add any more coins. If they tap Call, they will bet the same. If they tap Raise, they will bet more, until they bet five coins higher than what the previous person bet. Once everyone who hasn't folded bets the same, the person with the highest card gets all of the coins. Ace is the highest and 2 is the lowest.