ok. at first i thought this topic was going to end up badly but some of these suggestions are pretty good.
i don't really think any of the bosses in jRPG's or even western RPG's have been really MINDBLOWING. most of the time the battles are pretty set and stiff and most of the time the desirable EPIC feeling in the battle is unachieved. baldur's gate series had good attempts at this but only in a strictly tactical sense.
see, because of this, i think the best fights have indeed been in n64's legend of zelda - series or indeed SHADOW OF COLOSSUS. basically shadow of colossus took the boss fights of legend of zelda and made a whole game out of them, only punctuating the MAJESTY and OVERWHELMINGNESS of the fights.
it's kind of hard to explain but the rpg games can't achieve what these games did because there's so little control over the characters itself in rpg bossfights and most of the time a direct attack does SOMETHING to the enemy. DOES NUMBERS. this doesn't work in fps games (hl2 for example) or in these two games. even better, you can't even FIGURE OUT how to even damage the bosses in SotC at first so you pretty much just RAN LIKE HELL and hoped the best.
maaaan fuck adults fuck games. the water boss in SotC! my little brother who is only two years younger didn't want to do it because of the SEEMINGLY IMPOSSIBLE TO DAMAGE and the great tensed music in that fight. the area was just FILLED WITH WATER and you had no idea what to do. hsdfgsadgAIYFG the worse parts were when the boss seemingly RANDOMLY started to tail you jesus christghdaga. we ended up playing that with VOLUME TURNED OFF and GAMEFAQS. i felt like a huge jerk after that fight, i had spoiled something important right then
alsoalso the vanilla-hl2 had good ideas and mechanics for boss fights unfortunately it was mostly boring/disapointing as shit. the end fight was pretty bad.
also i have never fought giygas, i have heard it's a good battle??!! please do not spoil anything related to it i will fight it some day.
mgs3. the fury was gay as hell whoever thinks it's the best fight?!? get a grip man, smoke less!! no joke the fight against the end was one of the most immensive boss fights i have ever played. i really liked that fight. really neat! besides being a good fight in general, it somehow managed to break the rule of the boss fight's boundaries. like not EVOLVING... THE BOSS FIGHTS?!? but rather than breaking the unsaid rule of when the boss fight is ON or when it is OFF. ONE OF THE BEST BOSS FIGHTS for real
i kind of dismissed baldur's gate in my first paragraph but holy shit what a neat design in overal. both games without expansions are really well planned and scripted. my worst, most difficult fights have been with that game and they have also been the most rewarding ones too. you could try making your way through using certain glitches (the talk glitch was pretty bad but it was fixed in certain updates) and casting all the enchantments you could at the beginning of the big battles but really, in the end all of that didn't mean that much. if you don't know what you are doing or what you need to do then WELP. i wish i could explain this better.
sorry for a ragnar-like post also ragnar rules.
lolthanks
also I kind of mixed up memorable/IMPOSSIBLE boss fights and I still remember fighting Mike Tyson in Punch-out was like the most impossible thing ever in the history of things that are hard to do - I'm pretty sure like curing most diseases is easier than beating Mike Tyson without the game genie. Also Super Punch-Out had those guys who were brothers or something and they were EACH as hard as Mike Tyson I think - or like you beat the one guy and it's impossible and then the next guy is EVEN HARDER thanks a lot game designers. I might be completely wrong and the second guy is a total push-over like Glass Joe like thanks for playing the game etc.
also Giygas
I don't even remember who the fuck you fought against in most games - like last boss of Final Fantasy 27 what was he like an angel but sort of a devil and he had tentacles that throw swords at you and can like turn into your dudes and do shit that your dudes would do but it's not it's HIM
also Dragon Warrior 7 you fucking fight against God. And God knows HELLFIRE or some spell like that
also the final guy in Dragon Warrior IV was animated and crap and I was like WHOA I was easily excited as a kid