[General Discussion] Overly Frustrating RPG Boss Battles - Sephiroth kicked my ass

I'm kind of surprised I haven't seen a thread based on this subject. I guess I've been in a big thread making mood lately.

When playing an rpg I enjoy a nice good challenging boss fight just as much as the next person. Boss battles are never any fun when they're too easy and there isn't really any strategy involved. As much as I enjoy the odd challenging boss battle, there are sometimes boss battles (sometimes the final boss or a secret boss battle in some hidden dungeon) that are so overly frustrating you just lose to them so many times it ups your level of frustration to the point that you feel like putting your fist through the television screen.

I'm having that experience right now from a nice little extra dungeon called the Seraphic Gate from Valkyrie Profile 2. I can not pass the boss of the second floor of that dungeon, and the funny thing is I have a lot more bullshit to go through since there are 5 floors to the Seraphic Gate, so I'm sure when I eventually beat that boss, the next boss will be just as ridicolous.

To the Gamingforce Community, what have been some of the most anal retentive overly frustrating boss battles you have ever faced.

If you feel when talking about a specific boss battle might ruin an important part of the rpg story, please use spoiler tags where applicable.

Final Fantasy Tactics:

Spoiler:

Velius from Final Fantasy Tactics. I wasted too much time trying to get rid of the archaic demons, and by the time I killed two of them, Velius had already killed me. I lost to this guy literally 12 to 15 times before I finally beat him. I ended changing to a monk with counter and punch art to finally take him down. It was definetely a frustrating battle. My fiance warned me it was going to be a tough battle, but I didn't believe her. After trying to beat him after the 6th time I finally started to understand how frustrating that boss battle was.

Parasite Eve:

Spoiler:

Mutant Crab. I had always found a lot of the bosses in this challenging especially the first time I played it, but if it was one boss that frustrated me more than anything else was the mutant crab in the warehouse. It seemed like I could never dodge his bubble attack. It wasn't until my fifth try fighting I had finally realized I had haste, and using haste actually made this battle a little easier.

Final Fantasy X:

Spoiler:

Seymour Flux on top of Mount Gagazet. I was actually getting through many of the bosses in this game without much difficulty, but I actually found this boss fairly hard the first time I played Final Fantasy X. The boss fight always seemed to go well until I got this boss down to minimal hp and then he would throw out this massive attack with a lot of projectiles that literally killed my party every time. On the 5th or 6th try I finally managed to beat him by just throwing everything at him at once before he hit his critical hp level.

Keep in mind, I know for a fact that star ocean 2 tends to have the hardest boss battles throughout the majority of the rpgs that have ever been released. I just haven't actually sat down and played the game yet.

What have been some of the most challenging but frustrating boss battles you have ever faced.

Jam it back in, in the dark.