This page is for venting on bosses that gave large numbers of people grief. They do not need advice on how to beat them. They already know how to find GameFAQs.
The page isn't for you to talk about how great you are at the game either. Save that for your blog.
NOTE:Final Boss and Wake-Up Call Boss cannot be That One Boss without being overly hard by their standards. Please do not nonchalantly add them as examples. Bonus Boss is completely banned. They are supposed to be overpowerful and have no real standards.
Mr Freeze from Batman: Arkham City can be incredibly hard to defeat on higher difficulties, as his health and damage increase substantially between them, and consequently you need to use more and more strategies to whittle down his health. Since many of Freeze's coutermeasures prevent Batman from using important gadgets and skills, which makes the fight progressively harder as Freeze's health goes down. Furthermore, on harder difficulties, Freeze can kill you in seconds if he locks on to you, and he's absolutely relentless, and will constantly deploy seeker drones to trace your heat signature when he loses site of you.
Say Hello To My Little Friend from Hitman 1 is the hardest mission in the game, and the only target in the series to be inexplicably durable. First off, it's actually impossible to stealth through, as at some point, you will make yourself known. Then there's the objective to blow up the drug stash, which is protected by guards who will shoot on sight. Then you have to do a shootout against a coked-up Tony-Montana wannabe with a full-auto machine gun, who only goes down after filling him with his weight in lead. Then you have to make a mad dash to the plane while under fire. Oh, and this game doesn't have any way to save mid-mission, so you'll have to do everything all over again if you fail. Have fun.
This level becomes ridiculously easy, however, if you found the sniper rifle in the previous level. You can see him and snipe him through a window, and save yourself all that trouble.
This is an odd case. It takes less than ten shots with a pistol to kill Tony Montana. You just have to wait a while between shots. He has a period of Mercy Invincibility after each successful hit. If he doesn't say anything when you shoot him, you haven't waited long enough. It makes the fight easy but boring. The rest is crazily hard, though. It's best to kill Montana first after you've knifed everyone in the house in the right order, then go to the drug stash.
This is very similar for every game in the Hitman franchise. These days, it is considered that Hitman 2: Silent Assassin is virtually impossible to complete with the titular Silent Assassin rating, and the entire series is considered difficult. Somewhat averting this trope, however, in that most of the targets outside of Hitman: Absolution have about as much health and firepower as the regular mooks.
Metal Gear Solid 3: The End is enough of a That One Boss that Konami put in two different ways to defeat him without fighting. If you don't kill him at the dam or wait for him to die of old age during the boss fight, you're in for one of the toughest sniper duels in gaming. Prepare to spend a good hour fighting him. Finding where he's hiding without being spotted yourself is damn hard, as he's got fantastic camouflage. Picking a single spot and waiting in first-person mode to ambush him results in him knocking you out from behind. Letting him see the glint off your scope gets you a tranquilizer round in the eyeball. And don't expect him to sit still either; he's stalking you even while you're looking for him. And if you want to get the stamina-kill, you have to do this all with your tranq-pistol.
Let's not forget that he could shoot you while you weren't even playing the game. And he's even worse on boss survival (hard mode): He knocks you out with a single shot (to be fair, you also kill him with a single headshot), his position on the map is randomized and since you obviously want to beat the highscore if you even bother fighting him, you have to be fast about it. Oh, and as soon as you have a straight aim at him you have like 0.5 seconds to fire before he notices you and runs away.
Here's another handy tip for finding him, if 90% of the trouble you've been having is running around Sokrovenno South for hours just trying to find the bastard - did you know that The End fight actually consists of three different areas? That's right, those cliffs he's shooting from between long stretches of seemingly vanishing completely are actually accessible by you, the player, and all this trouble you've been having is your own damn fault for not realizing he can run through the loading screens into different areas unlike every single other boss in video game history. Completely frustrating, especially if the person you ask to kill (tranq) him for you only chooses to divulge this useful tidbit well after you've handed over the controller...
The Fury is a likely candidate. Early on in the fight, it's as simple as swerving between corridors and taking potshots at him. Soon enough, he gets pissed and starts going all-out with his flamethrower. Suddenly, he now always knows your exact position, and starts shooting his flamethrower down entire corridors. Not only does this give you a small margin in which to actually nail him with your weapons, but the fire also makes it a bit hard to even see where you're aiming.
The Fear is also difficult if you're trying to tranq him. Aside from his method of fighting (hiding in trees and jumping around to attack you with a poisoned crossbow), he will also hunt animals to recover his stamina, which is what tranquing depletes. He does this reliably when he gets low, so you have to find him and quickly finish the job before he can finish eating. Fail, and you get to fight him from what is essentially full health all over again. You can't even deny him a food source because that screen has the single most wild animals in it of anywhere in the game. (However, if you happen to have some spoiled food in your inventory, you can poison him, and if you find the Infrared Goggles...)
Psycho Mantis, who is fairly easy - once you've figured out the fourth-wall-raping puzzle you need to solve just so you can hit him at all, of course. He can still be a pain though with him throwing all of that goddamn furniture everywhere.
Sniper Wolf can be this on the first playthrough since you are unlikely to know where Diazepam is and without it, the PSG-1 is a pain to control.
That being said, the second time Snake faces Sniper Wolf is preposterously easy, as she can be taken down with Nikita rockets while Snake is safely out of range.
Metal Gear Solid: Peace Walker had the AI weapons, since they take so long to take down and some of their attacks can be real tough to dodge. However, the second battle with Peace Walker itself is probably the worst, since it will also sometimes start a nuclear launch sequence, in which you have one minute to damage it enough to stop it, or you get game over and have to restart the entire fight again. It also has EMP pulses which will stop rockets from hitting it.
Some of the custom vehicle fights, particularly the helicopter bombers, are incredibly frustrating, especially when you're trying to capture the damn thing intact.
Metal Gear Solid 4: Liquid Ocelot. Not because he's difficult, that's to be expected. It's because the game foists a whole new control scheme on the player. The only similar boss is the Rex vs Ray fight, which is hardly enough time to acclimatize to the timing and mechanics, especially since a 100-ton death machine controls a little differently than a CQC battle. Most of the frustration with Ocelot stems from the dodgy new dodge move, which is calibrated for an over-the-shoulder view....so naturally the first part of the Ocelot fight locks you into an overhead view and causes you to duck'n'weave straight into Ocelot's fist half the time. On the higher difficulties, this one boss can cause a no-deaths playthrough to start racking up the body count.
From Deus Ex: Human Revolution, Barrett, the first boss of the original version of the game. He has a minigun on his hand that will shred you in seconds, has a tendency to toss around grenades like they're going out of style, takes a lot of damage before he goes down, does not go down from nonlethal weapons, moves surprisingly fast despite his casual swagger, and you can't use your knockout or instant kill moves on him. And if you get to close to him? He'll use a version of that attack on you. And you absolutely have to kill him. You can't get out of the room until you do. To make matters worse, up till now you've probably been following a stealthy strategy to rack up points and avoid getting shot to death, so you might not even have any combat-oriented augs or lethal weapons to fight him withnote the game does provide throwable items and weapons in side rooms but that's little comfort for anyone who hasn't spent any time in the game actually getting proficient with them. This all counts for the original. In the remake it's somewhat more viable for people who haven't focused on a combat playstyle.