I recall seeing this earlier, where Zalbag actually has special sword skills that are like the Knight's Power Break, Magic Break, Speed Break, etc., but he doesn't use them for some reason. However, I cannot seem to find the info anymore, but I do recall if you check his skills when he is fighting with you it will say the names. I'll just invalidate that question though since I can't back it up.

And to answer Despotus's question, the final guts is Ultima, and it must be cast on you, either by an Assassin (i.e. Celia or Lede) or by an Ultima Demon, or by the last boss.