Blues is the 11th and Final opponent in all of Yie Ar Kung Fu. He is Oolong's evil double if you will and defeating him will unlock this achievement.
Blues fights just like Oolong, but that doesn't mean he is unbeatable. You'll want to make use of the "Punch and Jump" strategy against him at first. Use your Splits Punch move by pressing Down/Away + Punch as he gets close then quickly jump to the opposite side of the screen. Continue this until he has around 3 blocks of health. As the fight drags on Blues will become more and more aggressive. The last 3 hits are always the trickiest. This is where you must be careful about how you hit him. You should be able to hit a final Splits punch on him to where he will go into Fury Mode and attack at will. This is your chance to get in close to him and mash out any attack you can and hope you hit him twice before you takes you down. I found that Oolong's Away/Up + Kick move works well toward the end of this fight as well.