Single-Player Tips
In addition to winning battles, the object of single-player mode is to rack up points and unlock bonuses. When you choose a difficulty level, keep in mind that higher difficulty levels net higher points. You can also acquire lots of points by performing well in matches. For example, finishing a match with no damage earns you 5,000 points and using only "b" moves in a battle earns you an additional 5,000 points. Be careful, however, because using the same moves repeatedly results in a loss of 99 points.
Free-for-All Tips
In a free-for-all stock game, the goal is to lose as few lives as possible. Since the winner is determined as the last person standing, not KOs, you simply need to defend yourself and avoid battles. In a timed free for all match, however, KOs determine the winner, so you'll have to get your hands dirty. Keep an eye out for opponents who have sustained lots of damage, and attack them for a KO. When choosing a character, pick the strongest of the bunch, like Donkey Kong or Falcon. In stock and timed modes, avoid getting caught up in large brawls, as you're more likely to end up on the receiving end of combos.
Team Battle Tips
As with any team effort, working together produces quicker results. Work with your partner to attack one opponent at a time. This will result in faster KOs. Split up your opponents at the start of each battle. This will help you and your partner focus on one enemy at a time and it also prevents your opponents from pulling off team combos. Whenever possible, coordinate with your teammate to hit your enemies with team combos. Do this by timing your attacks to where they hit one after another, preventing your enemy from recovering.
General Cheats and Tips
After beating the game using each of the eight base characters, you will unlock the Mushroom Kingdom, a level based on the original Nintendo-era "Super Mario Bros." games. You can also unlock certain characters by finishing the game and practice tutorials. In the last battle of the game, you will face JigglyPuff. Once you beat her, she unlocks as a playable character. Likewise, playing through the tutorial and battling Luigi will unlock him as a playable character.