What was the hardest video game boss for you?

It's been a long time since I played so my memory may not be totally accurate, but the final boss in fatal frame 2. I rage quit it because it was a one hit kill, and before you get to them, you had to walk down a long hallway avoiding other enemies. It was like 5 minutes of work to get to the final boss only for him to hit you once and you have to start all over. So infuriating. The rest of the game was so much fun.