What was the hardest boss battle you've ever seen in any game?

1. lingering will(i forgot) or terra
2. kingdom hearts 2 final mix
3. high hp defense, high damage, extremely fast and mostly undamageable , unblockable attack and many more crazy thing

The True Conquerer from The Last Remnant.
It's a multi-phase fight with no breaks, beginning with his two minions, Castanea and Roeas. These two are already no joke, capable of quickly ending an unprepared party.

The Conquerer himself has many powerful attacks, but what really hurts is that he powers up once he drops to certain percentages of HP, drastically upping the difficulty. It took me almost a dozen attempts to take him down, needing to adjust my parties each time. No other boss fight comes close to the frustration and satisfaction of that battle.

Boss name: Most of them
Game title: Cave Story

Seriously. Fuck that game's boss battles. The final boss is so damn impossible...

The hardest boss battle I've ever beaten was the final boss on Max Payne 3, in the hangar...that took me somewhere in the vicinity of 2 hours and half a dozen Rage Quits to beat...the hardest boss battle I HAVEN'T beaten would have to be Demogorgon in BG II...I tried to beat that bastard dozens upon dozens of times but never seemed to make much of a dent on it :(

EDIT: The reason I found the final boss on Max Payne 3 so hard was because it seemed like such a HUGE difficulty spike...

I get stuck in bosses all the time, I'm really bad at it.
I never managed to beat Brütal Legend and I'm pretty sure I wasted over an hour on the last battle.
I'm currently stuck at the end of the first level of Wings of Vi, I'm starting to hate that f*cking dragon.

The final boss (I think) for Intrusion 2. Never managed to beat him, and if I try I just want to punch a baby in the face.

Crash bash - every boss does 1 Ko hit and some of them minions
And cave story - the robot-tank which I'm not sure can be hit, I die quickly.before him

I also have to say Demogorgon. In ever managed to beat that guy. However, I have started playing the Enhanced Edition of BG2 on Steam now and so I have a second chance.

Duhlahan from Golden Sun. He uses your own special attacks using your special power to attack you. If he decides he doesnt want to use your special attack he'll just wipe out all your djinn.

I can't remember oldest boss-fights but recently the most difficult was Cthulu in Magicka (one of DLC). He had EVERYTHING!!! Well, I couldn't expect less from mighty Cthulu.

Wiegraf/Belias from Final Fantasy Tactics. Not only is this guy a monster who just kicks your ass himself. The close quarters your party is limited to plays right into the hands of the monks who accompany him. On top of that, you have to fight several battles through a castle to even get to him, and you get the option to save right before this big battle at the end. Me, being the wee little tyke I was, had not discovered the magic of multiple save files. Final Fantasy Tactics taught me a lesson. Hard. Restarted all over again, and grinded my ass off before that castle, made two save files, and still had trouble with him.

To say the truth, i dont like games with boss battles, i hate them because they destroy my momentum and this is my way of seen it. I like a more realistic approach from a tedious challenge. Also i hate when you need to press random keys to survive.

Also because i dont remember the hardest boss i voted for Regenerating health which also i hate.

Space Rangers 1 and 2 bosses - since SR games are pure sandbox and only goal is to beat the bosses you can attack them once you find them but the trap is ... you have to lower their health to a point they get into a black hole(their hp will be stuck at 1/XXXX) and then you enter the black hole and destroy it there .... so 2 phase boss fight ... and why is hard?

1. In first phase you need your allies to help you down his health(even with top gear is hard to get it down because of other ships and the mothership got really good weapons). So yeah... you need to engage the boss with other ships which can be hard because of the enemy ships who can rip apart everything that isnt a ranger or military.
   2. Once done with 1st phase you engage into an arcade combat inside the black hole ... you have to constantly look for powerups and health recovers before the mothership gets to them
2. Before the boss dies he will contact you for a dialogue and if you get the wrong answer you end up in neverending loop - boss keeps respawning after you destroy it so if you didnt save up before entering the black hole you get fucked .

1. Finall Boss (dont remember the name)
2. The Legend of Heroes: Trails in the Sky
3. Three Boss fights in a row, that takes 30 minutes to beat each with a lot of 1 hit KO's. Of course if you fail in any of fights you have to start all over again, even if you beaten first two bosses you have to fight with them again. Never finished the game cause of that...

Kaymat from Paladins Quest. I swear, that was the first boss I ever wanted to throw my controller at the tv over.

My friend was fighting him for over 2 HOURS and still couldn't win.

Oh, the nightmares.

Shameful but I still haven't beaten the final boss of my favorite game, Beyond Good & Evil. As I remember it wasn't even that hard, but taken the fact that it was a boss battle (which I generally disliked in a game) thus knowing no "good" gameplay comes after it combining with me being uncaring toward the story and the feeling of completion altogether, I just left it at that. It's still on my bucket list to complete the game.

Aside from that, I'll say the final boss of Might and Magic: Clash of Heroes. I remember going for it for 2 or 3 days before I managed to kill him. The battle was the kind that needed not just the skill you gathered through the game but also luck. You needed him not to shoot the same coloumn twice or you had little to no protection from the blast.

i can't say it was the hardest, but it was when i solo the black dragon on tales of pirate ages ago with a cleric in lvl 55 gear... took me around 38hour of fight (yes, only one fight, extremely loooooong.......) it was so fuckin tedious that i won't ever ever do it again xD

Yellow face on advanced level of Minesweeper. Man, fuck that dude :/ I mean I've done it, but when he activates that two-squares-one-mine attack as a desperation move when he's almost dead... that's just all kinds of evil.

Those are all annoying, definitely voted the protecting NPC though, just because AI sometimes works against you and it's indescribably frustrating.

Very light spoilers for Titan Quest (not even worth using spoiler tags) .. Regenerating health...I remember playing Titan Quest (I think the main game) and I had a Druid (or was it called Nature or something like that) spec so I focused in pets and and healing (side spec was Death I think, for that Lich pet). Basically I did very little damage, especially without my pets. Unfortunately everytime I summoned my pets they'd be one shot by the bosses life leech spell so any damage they did and I did would get healed, and the bosses output was way too high for me to kill him without pets (he easily healed through my damage if he hit me with the life leech). In the end, I spent an hour or two across a few attempts and never got him lower than 90-95% life. Had to ask for help on the Steam forums and thankfully someone was close to me in level and we killed the boss together. Was rather upsetting that simply due to my spec choice it was practically impossible for me to kill the final boss (that being said, still a great game, just learn from my mistake and don't play healer/pet spec if you are playing solo).

Also I just played and finished Octodad, the final encounter was extremely frustrating (and other parts in the game) because how (purposely) bad the physics in the game are, I may or may not have accidentally disrupted my coffee mug and spilled coffee over my keyboard and had to spend an hour taking the keys off, drying it out, and putting the keys back in (screw those support bars for space key and other large keys..) :)

Frickin' first boss in Duke Nukem 3d. Never have been able to beat him. Bastard.

1. don't remember (last boss)
2. Legend of Dragoon.
3. 45 minutes! got it on the first try but it was exhausting.

f quick time events >.<

Sephiroth on kingdom hearts 2 i waited until i reached level 99 to have a chance against him and you should learn all his moves and how to move against them i took me a lot of time to beat him
Oh ... and Ares on god of war in titan mode (the hardest difficulty of the game in normal mode he is easy to beat ) so i don't know if it counts :)

Tiamat from Darksiders. She was just fucking impossible. I never finished the game because I never got passed her. But it had less to do with her than with the actual game-play mechanics of this god-damn game. More precisely, the aiming and throwing mechanisms of War's stupid tri-blade. Aiming that thing in order to catch fire and then hit Tiamat was a chore in itself, but it was made even more horrible by the fact that you had to pick up an explosive bomb and stick it to her first and the window you had between her throwing a devastating half a life-bar biting fire-ball was 3 seconds at best. Whoever designed this segment was a fucking sociopath. Not to mention that once she was done destroying all of those semi-circular stone pillars it was just fucking pointless to try and you had to just restart from the checkpoint. I saw on YT people did it, but I don't think it was with a mouse and keyboard... Simply mind boggling to me.