A Small Selection of Wii Cheats

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Change bowling ball colour

As The screen is fading to black for bowling, hold down the control pad until it fades to bowling for these colours:
Cheat Effect
Control Pad Up Blue Ball
Control Pad Right Gold Ball
Control Pad Left Red Ball
Control Pad Down Green Ball

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Wii Sports Unlockable: Tennis court
At the warning screen after selecting characters, hold down 2.

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Play Golf without maps or meters

To disable the power meter, map, and the wind speed indicator, press and hold (2), then make a selection at the "Select a Course" screen.

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Change the tennis court

To change the tennis court to the blue practice court, press and hold (2) at the warning screen that shows after selecting characters.

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Silver Boxing Gloves

After you've beaten the Grand Champion, Matt, in a boxing match you'll be able to wear silver boxing gloves. To do so, hold (1) when the screen becomes black before a boxing match.
 

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Bowling Ball Color Change
You can select your bowling ball color before you bowl by using the directional pad. When you reach the screen warning, 'Make sure nothing is around you', hit the A button and hold the D-pad (until the alley UI appears) to choose your color:

UP = blue
LEFT = red
DOWN = green
RIGHT = yellow
Hint - Tennis Pro Tips

When playing tennis and building your skill level, you can quickly gain skill points by setting it up so that your Mii is both players on a single side. After orienting yourself to this type of gameplay (it takes some coordination), you will notice that your wins will earn you 40+ skill points each time - basically double what you would have gotten if you had played with the computer on your side.

To do this trick: When you select which type of game to play, "Single Game", "Best of 3", or "Best of 5", it shows you which players are at which locations on the court. Your Mii's default position is the left side server. On the same side, use the A Button and click on the figure standing at the net. It will change from the "?" shadow to your Mii (assuming you are playing alone). Then proceed to pick which duration of tennis you'd like to play.

Note that you should ensure that you win, otherwise you may be at risk to lose double the amount of skill points if you lose.

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Special Bowling Ball

Get to pro level to unlock a bowling ball with diamond designs on it.
Wii Sports Easter Eggs

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Scare Crowd in Bowling

To scare the crowd while bowling, start the regular motion for bowling and let go on the backswing. The ball will fly backwards and the crowd will scream and jump.
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Amuse Crowd in Bowling

To make the crowd laugh in bowling, move to either of the gutters in your lane, turn into opposite lane, and bowl so the ball goes over the barier between the lanes. The ball will go into the gutter in the opposite lane and the crowd will laugh.

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Baseball
In baseball, before you pitch you can control all pitches using the d-pad. Be careful, because moving them too much results in a ball.

Courtesy: gamespot.com/wii/sports/wiisports/hints.html | cheatscodesguides.com/wii-cheats/wii-sports/ | news.softpedia.com/news/Wii-Sports-Cheats-and-Unlockables-Wii-46781.shtml | neoseeker.com/Games/cheats/Wii/wii_sports.html