Well, I haven't been to the official site in quite some time, but I remember it always used to say that prolonged contact with the dark side of the force caused him to look like that. With some stretch of my imagination, I was able to convince myself that that could mean p;rolonged contact with his own force lightning. I would have preferred something a little more subtle, bu t that's a bit too much to ask for, I'm sure. And I posted earlier today in another thread that I too thought that Yoda and the Emperor were above all th is swordfighting crap, that they'd transcended to a higher plane. I could see them dueling like they were in Sith but only to have the Emperor throwing chairs while Yoda repelled them. Seeing Yoda jumping around and sp8inng like a top just gets kinda old after a while and completely makes a mockery of his "knowledge and defense, never for attack" line.