Glover for the Nintendo 64. On the last boss, Frankenstein, and I didn't beat it until years later as a teenager. Little kid me couldn't figure out how to defeat it. Actually I can't really remember if that was the last boss, but it was definitely one of the later boss fights in the game.
It took you 12 tries to beat O&S and 6 hours to kill Rom? Wow, so odd. I was stuck on O&S for days but it didn't take me more than half an hour to kill Rom...
The one boss that has given hell to me so far in BB is the Abhorrent Beast in the layer 4 chalice. I ended up cheesing it with poison knives...
I didn't beat King K. Rool on DKC1 for years when I was a kid. I later realized he is one of the easiest final bosses ever. On more modern times, Ornstein&Smough gave me a really hard time on DS, almost quit the game. Thankfully I found out I could ask the help from someone grossly incandescent.
Ornstein and Smough took me about 4 hours over about 5 days.
Beowulf from DMC3 took me 2 hours or so one night to get passed.
Special shout outs to the final boss of Persona 3 for being the longest single battle I've ever fought, a bit less than 1 hour.
The Harrier from Metal Gear Solid 2 on European Extreme immediately comes to mind. I was stuck on it for a number of weeks during a "Big Boss" emblem playthrough. The timing is absolutely brutal on it and you don't get any second chances if you get hit at all. It's a fight that can be over rather quick once you get into a rhythm with it, but it requires pretty much perfect timing and positioning making it very challenging.
Bogimoray in Lost Odyssey is the second boss to come to mind. It has been awhile since I've played it, but my recollection of the boss for anybody who isn't familiar is that it features a gigantic worm like boss and a number of smaller minions. It uses the minions to charge a paralysing attack that stuns your party and allows a huge amount of damage to be inflicted to you. The secret to beating the boss is that an anti-paralysis item can be found prior to the boss. This status affect can be learned by a number of the individuals in your party, and make Bogimoray quite easy. Unfortunately, in my first attempt of the game, I managed to miss this item, and spent hours trying to beat Bogimoray to no avail. I eventually had to reload a save from far earlier to beat him.
Ninja Gaiden 2 on Master Ninja also comes to mind, but I cannot remember which boss it was that posed the problem. I have a feeling it was Genshin in Chapter 2, but I cannot recall. Genshin in Mission Mode also posed quite a problem because of the extremely small arena and the Incendinary Shuriken Ninjas that accompany him.
That part in BioShock Infinite when you fight like infinitely respawning ghosts in a vault or whatever. I remember my main strategy was to keep luring in ghosts while I fought the main ghost or something like that from behind cover. I ended up collecting so many ash piles they the frame rate went into the single digits and I had to just keep going.
There was a Xenosaga Episode 1 boss that I think I fought for about 45mins-1hour because it was strong/resistant to the attacks that my current party had so I was doing single and double digit numbers when I should have been doing triple digits.
fight in Mt Valac for the longest time in Xenoblade Chronicles. Can't say for sure how many attempts, but that boss and the 6th stage boss in Catherine also kicked my ass for a long time.
Remember that boss battle in The Force Unleashed where you have to fight that Star Destroyer? It took me nearly two weeks because the keyboard controls were so shitty. After 12 days I ordered a xbox controller from Amazon and finished it.
Originally it was O&S. Dark souls was my first souls game and I only just about knew what I was doing and my build wasn't that suited. In the end after several nights of trying I summoned the NPC and took them down. I later came back on NG+ and soloed them after 1 or 2 attempts with my since improved build.
However now it's Ludwig on NG+++ with an under leveled character with terrible gems. Took about 6 hours but it felt amazing when I finally did it.
I never really found the ones a lot of people complained about hard. Rom I just killed the spiders first and it was a joke how easy it is. Watch dog I got on attempt 3. It has a pretty small moveset so wasn't really hard, just took time due to the amount of health it has. Headless beast I just stayed near his legs and was easy and ebrietas I just jammed my self up her arse and she pretty much couldn't hit me.
The only dark souls 2 DLC boss that was a challenge was the fume knight for me but even then it only took 11 attempts (was 1 hit away on attempt 5 though but got greedy lol).
Originally it was O&S. Dark souls was my first souls game and I only just about knew what I was doing and my build wasn't that suited. In the end after several nights of trying I summoned the NPC and took them down. I later came back on NG+ and soloed them after 1 or 2 attempts with my since improved build.
Took me a week or two of practice to be able to beat Mushihimesama Futari Original Modes final boss Queen Larsa for the 1 credit clear. Ppl who aren't into shmups will probably know her from "Hardest Video Game Boss Ever" You Tube Vid although Original Mode is a million times easier than Ultra mode in the vid.
There are several other shmup bosses I've spent about a week on too but Guwange's sticks in my mind due to not beating it (damn that final random bullet pattern)
Hmm...for consecutive attempts? Hexos from WoW. FUCK. THAT. THING.
One day, I'll explain how I actually did beat him. That's a funny story in itself.
Go look up how many deaths that bastard has caused in the game.
It's a pretty big number in comparison to any other boss from the Brawler's Guild.
You really don't wanna know how much time I spent on him.... >_>
Longest single battle? Hmm...that's a tough one. I'll have to think about it.
Anywho, here's a related story:
-Barbatos from Tales of Destiny Remake: TONS of attempts; the Bonus Dungeon only allows you to a number of characters per floor, and for the last floor, this unfortunately carries over to Barbatos.
Anywho, I screwed up and made a save right before the fight with a less than ideal team with no way to switch my team out. (I had a few Narikiri Dolls, but I had to go in and reconfigure EVERYTHING for each attempt, since I couldn't make another save.)
I spent hours trying to beat him, but to no avail, so I eventually had to just the Bonus Dungeon over from scratch (which for me was like a 2-3 hour ordeal getting through the whole thing).
After that, I stopped playing the game for about a year, then came back to it one New Year's Day. Went back in, did things right, and went up against Barbatos with a much better team and stunlocked/juggled his ass to death.
(Bloodborne) all nearly broke me. Logarius, also from Bloodborne, nearly drove me mad with his massive buff and salad bar of RNG until I learned about charge attacks and back stabs, at which point he was trivialized.
Over a period of two months, two days a week at 3 hours a time, turn 9 in ffxiv. Drove me up the wall, actually roared in triumph and deafened everyone on our TS channel when we won.
Getting all the dogtags in MGS2 on extreme and ending up fighting Solidus where I couldn't take a hit without dying. I remember giving up for a month out of frustration. Finally got the completely useless blue wig in the end.
Four Kings in Dark Souls and the bloody run you have to make each time to get back to them lingers in my mind. Ornstein & Smough also deserve mention - oddly it was during my second playthrough (new character) that gave me the most problems.
I Wanna be the Guy - basically all of them but Birdo was the one I remember almost breaking down on.
In terms of for a single once through fight, Yiazmat from Final Fantasy XII. Wasn't hard and I had gambits set up to do the majority of the fight while I browsed the internet. I wasn't aware you could save during the fight and his HP wouldn't recover so things got tense towards the end. Penance in X was also a also a fairly long affair which I remember taking a break from midway through.
