This solution requires two controllers. One of them needs to be a turbo controller. If you do not like solutions that involve turbo controllers, please just hit the back button.
Text is below the video if you prefer text over video:
P1 will be turbo, P2 will be the other controller. First, go into options and turn off vibration. Go to versus, P1 select Po, P2 can be any character. Press X to go to options and change Lives to 1.
Start the game, on P1, turbo Y button and push the left thumbstick to the right (use a rubberband or heavy book).
Wait until 50 matches, 100 matches, 200 matches, and 1000 KO achievements unlock. You can also unlock 10 team matches and 10 stock matches if you enabled team mode.