Yie Ar Kung-Fu

This unlocks upon defeating Feedle, the 5th opponent in the game. You will face him right after defeating Pole. Once you defeat him and his minions they will scurry away like the cowards they are and then this will unlock.

Defeating Feedle

This is more of a Bonus stage where you must defeat Feedle and his team of clones, there are 10 in all. They will come at you from the left and right side of the screen and you will have to fend them off by pressing Toward them + Kick, Punch may also work. Each clone only requires one hit in order to be defeated. Focus on the ones that are closest to you because if you don't time the kick properly you will lose health. It can be fairly easy to pick up the Perfection achievement here if you're quick enough.