Seymour Guado's Third Form from
Final Fantasy X.
This guy was cheap as hell. For starters, he's fast; so fast, that he
always goes first (even faster than Tidus). He also takes two turns in a row, something that is not uncommon for bosses about 3/4 of the way through a game, but it's the following combo of actions that really make it annoying.
First, he strikes with his spear and anyone hit by it will be afflicted with the Zombie status. It's only negative downside is that healing and reviving have opposite effects. So his second action is a no-brainer; he cast Full Life on a Zombie target, which results in an instant kill.
So if you did not prepare with Zombie resistant or Zombie-proof equipment, you will be at a severe disadvantage in the beginning. Plus, you might need grind a bit; he ain't easy to take down.