Avatar: The Last Airbender - The Burning Earth
During the very first fight in the game, you will face a couple of enemies. Take these out in any way as you wish. After that you've killed them, a cutscene will occur showing you General Fong. Once it's over, you'll have four enemies running towards you.
Center yourself on the middle of the area you're on, and keep tapping B towards the enemies. Make sure not to get hit, but this shouldn't be a problem. Once you've hit the enemies 50 times, this will pop and will also be your final achievement.
If you would get passed this part and somehow not have gotten all the achievements, I strongly recommend that you restart the level/game and try again, as this is undoubtebly the best and earliest spot to do this!
Aren't you just proud of your accomplishment?