You're right about the (SPOILER)blood swords, however, (SPOILER)Emperor isn't a very hard boss to beat. It's a somewhat anti-climatic confrontation after taking on (SPOILER)Beelzebub, Tiamat AND Asteroth all in one sitting. Just use your strongest magic and attacks and he'll go down without much of a struggle. I'd say that either (SPOILER)Tiamat or Asteroth is the hardest battle, and since those bosses are completely optional, I consider them to be the mega bosses of FFII.