after getting the tournament champion achievement (winning the tournament with 20 characters) you should have roughly 900 or so KO's. You can boost the rest under 2-player with second controller. Pick Gorilla soldier because he has the most powerful punches and use someone small to beat-up (like shifu or mr. ping) change the options to KO match and set KO limit to 10. use any area you wish. I used jade palace because it had a smaller platform. you have to hit the other character off the screen. just running off the screen to die counts as a suicide NOT a KO. Each match to 10 takes about 5 min.