Hint: Quick Replay
Once your shot has stopped, press B to watch an immediate replay. The angle will change each time you view the replay. Press A to speed the ball up during the replay.
Hint: Better Players
To get better versions of each player, accept their invitation in Character Matches Mode and defeat them. Note: You'll see an envelope next to the character with an invitation. Only beating characters through invitation earns you upgraded stats for that character!
Hint: Change Weather
Save your game and then reload it. The weather is randomly generated each time the hole loads.
Hint: Super Spins
When setting the accuracy meter, there are four types of spins you can apply depending on your button combo press. You must enter the combo quickly:
A, A: Normal topspin
B, B: Normal Backspin
A, B: Super topspin
B, A: Super backspin
Hint: Taunt Your Opponent (Or Being Obnoxious)
If playing a multiplayer game (with multiple controllers), press any button or use the C-Stick when it isn't your turn to taunt the opponent. Each character has four separate taunt phrases/sounds. Pressing and holding a button and moving t.opeeft analog will yield more (and nastier) phrases.

When you taunt you can either use the C-stick for nice taunts or the D-pad for evil taunts. This makes it easy to do multiple taunts for maximum annoyance of other players for when you want the others to screw up in really competitive games where heavy bets have been placed. Just roll your thumbs on the d-pad and c-stick and it will make their mind twist and flip.

Hint: Restart Hole
At any time in any one-player game mode that allows you to save (i.e. Tournament Mode, Character Matches), you can restart a hole you're doing poorly on. Save the game and when you reload you will begin at your drive and all uses of Power and all shots will be erased, giving you a second chance.
Hint: Reset Pin Location
Don't like where a pin is located? Save your game and when you load it up the pin will be randomly relocated.
Hint: Pikmin at the Peach Invitational
During the Peach Invitational, if your ball lands in the yellow flowers you will hear a weird noise and see small Pikmin fly out screaming. Press B to see an instant replay of the action!