Yoda beats the emperor because the emperor is a bloody coward. Okay right before the fight empeor trys to leave(Yoda stops him) at the end instead of looking for yoda himself the Chicken emperor sended clones to look for him. You might say Yoda ran off, but he was throwing everything the emperor had back at him. at the end he fell further because he was unlucky to be on the edge and emperor in the middle.