Final Fantasy X-2 - Sphere Break
Sphere Break can be a rather confusing game when you first start playing. You don't really have to worry about your opponent so much as the time and turn limits. If you don't fulfill your coin quota in the amount of turns specified at the beginning of the match, you lose. If you take longer to make your move than the turn timer allows, you automatically forfeit the match. In essence, you're really going up against yourself.The game's tutorial should give you a good enough idea on how to play the game, but if you try to play by the simplified rules they give you, a lot of the opponents you'll encounter in Luca will easily smoke you. To be able to hang with these players you'll have to use two game features to your advantage: Coin Count Echo Bonus and Multiplier Echo Bonus.
The Coin Count Echo Bonus is by far the easier of the two to pull off, especially during the Sphere Break tournament in Chapter 3. The Ahriman Coin has this trait, and is one of the more common coins you can acquire. This coin will be among the ones you are given to use during the tournament. Once you have a coin with the Coin Count Echo trait, use it as one of your four entry coins. To get a Coin Count Echo Bonus, you have to keep using the same number of coins to get your target number multiple. For example, if you get a Core Break by using 3 coins, then get the next Core Break by using the same number of coins, you'll get a coin bonus for repeating the number of coins you use. The bonus is based on the number of Border Coins you use, so if you use only Base Coins you won't receive the bonus. The more times you can pull this off in a row, the bigger your Coin Count Echo Bonus will become. This tactic comes in handy when taking on Shinra at the tournament.
The Multiplier Echo Bonus is harder to execute, and there aren't as many coins that have the trait. If you use the same multiplier to get a Core Break, you'll earn a coin bonus. For example, if the core number in one round is 4, and you get 12 as your multiple, you would have used the number 3 as your multiplier (4 x 3 = 12). To get the Multiplier Echo Bonus during the next round, and the core number is 6, you'd have to try to get 18 as the multiple, since 6 times 3 is 18.
Both methods above really help shift the tide in your favor during a match, but even they aren't foolproof. The game loves to throw you a curveball by making 1 your core number. If this happens, you'll get the Core Break but any Echo Bonuses you were working on are out the window. Don't get discouraged, even if it ends up costing you the match. There's always the next game, or, if you really despise losing, there's always the option of resetting the game.