Progression basically like doing A6S. Which was one of the harder fights to progress on because it was basically 4 fights in a row to progress on the next boss you had to keep beating the previous bosses just to try the next boss. Ultimate is like 3 separate fights in a row. It would definitely be easier with checkpoints. I actually like the check point in O4S. Imagine how much harder that fight would of been with out the checkpoint.