During Disc 3 in Alexandria you can play a mini-game with the Nero brothers from Tantalus. It's very similar to the shell game. Zidane will place a bet then the Nero brothers will shuffle places and you'll have to guess who is who. They'll say point out "name" and you say "left", "center", or "right".

After a round you can choose to take the gil or continue to raise the amount you receive. But remember that if you guess incorrectly you will loose all the gil you've bet. Also, the brothers will increase their speed for each time you choose "continue". You can win up to 25,600 gil in this game.