Actually killing the executioner on the FIRST run through was very tough. In actuality, the Uroboros were the easiest, since all you had to do was burn the heck out of it. Excella was the only boss to actually kill me though, but that was because Sheva got smeared. All in all, my favorite bossfight was the one against U8. Something about a giant crabs feels so right, and normally crabs are annoying as heck.. lol