Switch bowling ball color
As the screen begins to fade to black (while bowling), hold down the control pad until it fades to bowling for these colors

Control Pad Up - Blue Ball
Control Pad Right - Gold Ball
Control Pad Down - Green Ball
Control Pad Left - Red Ball

Change 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.

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.

(Cheat Via: GameSpot)

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