I Am The Hero

To unlock this achievement you have to defeat the boss Blah-blah. You will face him normally during level 3-3 of the Story Mode. He will also appear on the Arena Mode. Hes pretty easy just pummel him as quickly as possible and watch out for his golf style swing that can damage you pretty bad. Should be easy enough, each boss is a save point so if you die you don't have to repeat the level.