Physically, probably Liebgott in Band of Brothers. One, we had to be soldier fit, but two, I had to get to the same size as him. He was 130lbs, I got down to 135. But it was also a legacy that we wanted to get right, so that was something we all took very seriously. Others were challenging in terms of learning fight sequences like The Beautiful Ones knife fight, or the Green St sequences. (esp the sequel)