The King of Fighters XII

This achievement is for clearing arcade mode using only Duo Lon, meaning you can't lose a round with him or else you'll avoid the achievement. Keep a second controller handy to prevent any untimely losses, and set the difficulty to easy and the time to 99 in the game settings. The time is key because any wins by time out immediately null your achievement.

Also, I found that simply pressing YYY (default controls) made for a rather strong triple punch that made each battle easy. Also, if you'd like to keep some distance forward and X gives you a stretchy punch that isn't too powerful but keeps you away from the opponent. The best move however is forward and A, as it gives you a poke at any distance. If you want to increase the gap between yourself and the opponent do backwards a and it's like a dash only better! Using the YYY if the opponent gets close paired with this made my run relatively simple.

If you're going for a completion of the game, it's good to note which characters you have defeated for future reference when going for the KO'ing each character with all characters (King of Fighters).

Beat the game with Duo

Have to win with only him, KO everyone and use no continues.

If you are in trouble use the second controller when you are about to lose to get a restart