To unlock this achievement, you have to win 200 matches. This officially means that any and all matches you win will count towards the achievement, whether it be in single player mode against the AI, against a human opponent in a local setting or against a human opponet on Xbox Live.
The way I unlocked it is to meet the neccesary conditions to unlock the other 11 achievements and then went to UMK3 and do single player on the Novice Ladder. From there, i pick Sonya, whose Leg Grab move is spammable up to a certain point and keep on playing until I lose a match. From there, i let the continue timer (and whatever timer there is to unlock the three hidden characters) run out and then start again.
An intermediate player can get around 2-3 wins in a row on the novice ladder before the AI goes Ape**** on them. Keep doing it until the achievement unlocks itself.