->''I can't defeat [[VideoGame/MegaMan2 Air Man]].''\\
''No matter how I try to dodge his tornadoes, he just kills me again.''\\
''And even though I can get behind him''\\
''It's no use, I try to fight, but I get blown away in the end.''\\
''I shoot as fast as I can,''\\
''But when I had to go against Air Man's tornado I was helpless again''\\
''I'll try again, of course, but this is my plan:''\\
''I'll keep my [[EmergencyEnergyTank E-Tank]] safe in reserve just as long as I can!''
-->-- '''[[http://www.youtube.com/watch?v=pjLouGft9kY I Can't Defeat Air Man (Kiwi Kenobi English Version)]]''' [[note]] For the original Japanese version, [[http://www.youtube.com/watch?v=YPGIkY4PyQ8 click here.]] [[/note]]

There are many different categories of bosses, some more memorable than others. There's the GiantSpaceFleaFromNowhere, there's the ClimaxBoss, the FinalBoss...

And then, there's That One Boss, the boss that falls victim to poor playtesting or was thrown in by especially cruel developers. You're levelling up normally, plowing through every battle, until you reach this particular battle and suddenly meet a nasty road block. Eventually, you RageQuit, or you go on the Internet looking for assistance. In the event that you stop by the game's message board, lo and behold, everyone else is having the exact same problem, with entire topics asking "how do I beat That One Boss?". Walkthroughs usually list the worst offenders as "[[TheDreaded the hardest boss in the game]]", and eventually, such a beast receives a reputation for being just that freaking hard. A few of them [[BestBossEver may be awesome]], but that still doesn't mean you won't be chewing on the controller in frustration despite it.

Certain types of boss are not usually included in this consideration right off the bat: The FinalBoss, WakeUpCallBoss, and BonusBoss. People expect the FinalBoss to be tough ([[AnticlimaxBoss usually]]), and the BonusBoss is usually included solely to be difficult. Players will prepare for the Bonus Boss by overleveling, but for maximum frustration, That One Boss needs only to [[GiantSpaceFleaFromNowhere just show up out of nowhere, preferably having no place in the storyline beforehand.]]

They usually show up in [=RPGs=], though they're not exclusive to them. Game designers will sometimes go out of their way to put them in, [[BeefGate serving as a bottleneck]] to make sure you spend a couple hours LevelGrinding before you go on to the next area.

Occasionally, the identity of That One Boss varies depending on an individual's playing style - bosses are often designed to have issues with one particular strategy, so one that requires another strategy can seriously hinder a gamer if they're not prepared to switch up their tactics. Please take a second before adding examples to make sure the issue is actually with the boss and not that your tactical decisions were just poor - if it's hard because it requires strategies you wouldn't have thought of then that can qualify, but if it's just because you hadn't mastered regular blocking timings or got the wrong end of the ElementalRockPaperScissors system then please refrain. However, any easy tactics like OutsideTheBoxTactic disqualify a boss from being That One Boss... unless the 'tactic' itself is [[GuideDangIt impossible to find]].

They are sometimes called the "brick wall boss", for obvious reasons.

Compare DemonicSpiders, which is more of a That One RandomEncounter, as well as the BossInMookClothing (we'll leave it up to you to decide which is worse). Most likely to be the one to use ThatOneAttack. See also ThatOneSidequest and ThatOneLevel. Contrast AntiClimaxBoss, where the boss is underpowered/easy for story reasons (or despite them), and BreatherBoss, where the boss is just pathetically easy unintentionally. For bosses that are not technically difficult, but are downright frustrating, see GoddamnedBoss. For bosses that are deliberately impossible to beat, see HopelessBossFight. If you're looking to read up on unfair bosses that the game seems to [[TheComputerIsACheatingBastard deliberately give every known advantage to,]] requiring you to either get by on [[LuckBasedMission luck]] or [[NotTheIntendedUse cheap gameplay]], head on over to SNKBoss. That page is for brokenness - this is just plain hard.

To sum it up. If the boss is difficult when you first get to him, but when you get enough skill (or understanding of the needed mechanics), it is easy on further playthroughs it is merely a WakeUpCallBoss. If it requires a very unusual tactic to win, but dies easily to it, that is OutsideTheBoxTactic. It has to be much harder than expected for that point in the game, and remain that way every time you replay the game to qualify as That One Boss. In other words, this is the boss whose battle will haunt your nightmares every time you see their image or hear their name.

It is useful to note that, as its name implies, most videogames only have ''one'' That One Boss. If a game appears to have several candidates for the title -- especially if ''every'' boss battle feels this way -- you are probably looking at EasyLevelsHardBosses, or a game that is just plain NintendoHard.

'''NOTE:''' FinalBoss and WakeUpCallBoss cannot be That One Boss without being overly hard by ''their'' standards. Please do not add them as examples. An EarlyBirdBoss will almost always qualify as That One Boss as well, but for reasons of the player's weakness rather than the boss's strength, so those bosses are better placed in the EarlyBirdBoss article. BonusBoss is completely banned from this page (though Rhythm Games are handled differently; see its section for why), as they are optional and they have to be overpowered. There is no measure for them.
See also: {{That One Level}}

Because there are so many examples of this trope, they have been categorized by genre for your viewing convenience.
* ThatOneBoss/{{Atlus}} (no, this isn't a genre, but a company. Yes, a company makes games with so many sadistically hard bosses that it [[UpToEleven needs its own section]].)
* ThatOneBoss/{{Action}}
** ThatOneBoss/MegaMan
** ThatOneBoss/{{Rosenkreuzstilette}}
* ThatOneBoss/BeatEmUp
* ThatOneBoss/CardBattleGame
** ThatOneBoss/YuGiOh
* ThatOneBoss/{{Driving}}
* ThatOneBoss/{{Fighting}}
** ThatOneBoss/{{WWE}}
* ThatOneBoss/FirstPersonShooter
* ThatOneBoss/{{Rhythm}}
* ThatOneBoss/{{RPG}}
** ThatOneBoss/DarkSouls
** ThatOneBoss/FinalFantasy
** ThatOneBoss/KingdomHearts
** ThatOneBoss/{{Pokemon}}
** ThatOneBoss/TalesSeries
** ThatOneBoss/WorldOfWarcraft
* ThatOneBoss/ShootEmUp
** ThatOneBoss/{{Touhou}}
* ThatOneBoss/StealthBasedGame
* ThatOneBoss/{{Strategy}}
** ThatOneBoss/FireEmblem
** ThatOneBoss/SuperRobotWars

!!!Miscellaneous Examples
* ''Literature/LoneWolf''
** The Chaos-Master from the 11th book in this series of gamebooks. It's a hideously hard fight if you don't bring the Sommerswerd along. If you do? Chances are you will die horribly. There's a particularly infamous Let's Play of Book 11 that had the players redo the Chaos-Master fight ''twenty-seven'' times before they finally won. It's that hard.
** So hard that pretty much everyone forgot about the series' FIRST killer enemy, the Gnaag Helghast. If you have a decent base Combat Skill, the Sommerswerd, and Psi-screen, it's a fairly challenging fight. If you ''don't'' have a decent basic Combat Skill... well, it's immune to Mindblast, so you're looking at a Combat Ratio of +1 under the best of circumstances. If you ''don't'' have the Sommerswerd, you can't do double damage. If you ''don't'' have Psi-screen you lose 2 Combat Skill points ''every round''.
** The Vordak fight on the skyship deserves special mention. If you don't have the Sommerswerd, you have a grand total of four rounds to win ''two'' fights; fail, and the skyship explodes and you're toast. If your starting Combat Skill is too low, it is [[UnwinnableByDesign IMPOSSIBLE to win this fight]]. It was so bad that Joe Dever gracious extended the time limit to six rounds in the Mongoose Publishing re-release.
** Bested the Gnaag Helghast and those annoying Vordaks? Well done, now get ready for Zakhan Kimah! If you have the Dagger of Vashna, you can settle this with a single do-or-die throw. Otherwise, prepare for a combat ratio of at ''best'' -3, and he has 40 Endurance. Oh, and if you have the Sommerswerd, he's also immune to psychic attacks.
** Then there's Darklord Kraagenskul. Have the [=DoV=] and a reasonable number of Combat Skill boosts? Somewhat tough, but managable. Don't have it? Prepare to fight crypt spawn, then make a do-or-die lunge for his sword (although if you're successful, Kraagenskul isn't extremely tough). Have the Sommerswerd? You have a time limit to beat the crypt spawn and ''then'' have to make a do-or-die sword throw, otherwise you'll get killed even if you defeat Kraagenskul.
** And ''then'' there's Ixiataaga, who comes at you with a Combat Skill of ''60'', and also at the tail end of a number of challenging battles, including Tagazin.
* Not actually a game example, but in the manga ''Manga/TheWorldGodOnlyKnows'', Keima Katsuragi can capture any girl... ''any'' girl... with the exception of Yui Goido. He himself notes she is a serious player, introducing a new meaning to Player vs Player. [[spoiler:He eventually wins... by playing the DistressedDamsel.]]
* Ashley's boss microgame from WarioWare Touched features borderline BulletHell patterns of projectiles to dodge and an end boss that has three separate pieces shooting things at you.
** In Warioware Twisted, all you need to know are these six words to know you're in trouble: "Ladies and gentlemen: Wario de Mambo!"
* While the final bosses of the ''Franchise/AceAttorney'' series usually take longer to break than other culprits, the final showdown in ''Investigations'' gets special notice for being so long and difficult that there's a save point ''in the middle of the fight''. [[https://www.youtube.com/watch?v=YpgPCGmTuew And here's a song about how difficult it is.]] Amusingly enough, the song in that link is a parody of the Air Man song that is the page quote.
* The MassivelyMultiplayerOnline game ''SDGundamCapsuleFighter'' has three of them.
** The first is the [[Anime/MobileSuitZetaGundam Psyco Gundam]] in the "Kill Three Psyco Gundam" mission, due to the fact that, at harder levels, it has infinite special attacks and, thus, it will gladly go into its BeamSpam special to prevent being killed. Even more frustrating when it does so at its last sliver of life with only 10 seconds left in the match.
** The second is the [[Anime/MobileSuitGundamThe08thMSTeam Apsalus II]] from the "Destroy the Apsalus II" mission. Not only does it have a stun beam weapon and an ability that reverses your controls temporarily, it's flanked by two [[Anime/MobileSuitGundam Acguy]] [[TheMedic Repair]]s meaning that if you don't kill them off ASAP, it'll just keep regenerating its HP while it keeps hitting you with beam weaponry.
*** What makes the Acguy Repairs even more of a pain is that they're one of the few units with Auto Lock-On Jammer (which disables Auto Lock-On when the unit reaches 30%), thus you're resorting to the old Eyeball Mk I to shoot these guys down!
** The third is the [[ANime/MobileSuitGundamSEED Aile Strike Gundam]] from the "Test Factory" mission. It spends 9/10ths of its time boosting around the boss room in the air and, as you're trying to shoot him down, you're attacked by [[Anime/MobileSuitGundam Balls]], [[Anime/MobileSuitZetaGundam Hizacks]] and [[Anime/MobileSuitGundamSEED Astrays]], as well as missiles that will outright stun you in your tracks.
* ''TabletopGame/{{Exalted}}'': second edition [[OmnicidalManiac Deathlords]] are ''hugely'' overstatted and obnoxiously powerful, to the point where people can wonder in all seriousness why they haven't destroyed the world yet. They were nerfed multiple times, most notably when their [[GameBreaker wtfhax perfect defense that didn't count as a Charm activation]] was clarified to only work a handful of times before having to be reactivated, but they remained ridiculously powerful.
* ''VideoGame/{{Minecraft}}'':
** The [[FinalBoss Ender Dragon]] falls into this category, especially notable in that it was the only boss before version 1.4 was released. It flies out of sword range, likes to knock the player off of things, usually off of the of [[FloatingContinent The]] [[FinalBossNewDimension End]] and into the [[BottomlessPit void]], and regenerates health whenever it goes near an undestroyed Ender Crystal, located on the tops of ''very'' tall obsidian pillars.
** The [[EldritchAbomination Wither]] is an even worse offender. It is capable of ''killing you and all your friends and allies before the fight even begins'' by releasing a massive explosion from its body. The actual fight is no better, it flies around and spits exploding skulls that also gives any target it hits a 'Wither' debuff, with said debuff draining their health bars, but unlike normal poison, this debuff will kill the target instead of leaving them with 1 HP, and thanks to the Wither being a three-headed monster, it can spam the skulls as well as attacking multiple targets simultaneously. You can snip it with arrows in the first part of the fight, but after half of its health is gone, it gains a shield that makes it immune to said arrows, leaving you with Splash Potions of [[ReviveKillsZombie Health/Healing]] and your swords. And if you try to hide? The Wither will ''eat through blocks you're hiding behind''. Did we mention it has a HealingFactor?
* ''{{Nintendo Land}}'s {{Pikmin}} Adventure'' attraction has mostly average boss difficulty... except for the Emperor Pinchipede. For his first phase, he has about 7-9 weak points, some big and some small. When you take out a small weak point, it disappears. But when you take out a big one, it stays on the field, acting as a spinning disc of doom that wanders about and damages you if you touch it (but not the boss). You must take out all weak points to move to the next phase, and it moves too fast to be able to reliably aim at any specific weak point, so you'll most likely hit the big ones and have 4 spinning doom discs on the battlefield while you continue to toss pikmin at the small weak points. For the sake of saving space, I won't go into the other phases, but know that they are both worse.
* VideoGame/WinnieThePoohsHomeRunDerby has a bunch of these.
** Kanga and Roo start to bounce the balls, which can be frustrating when you're used to the ball coming straight at you.
** Rabbit throws the ball really slowly, and then the ball comes REALLY fast at you. If you're playing against him the first time, you'll freak out.
** Owl zigzags the ball and the ball comes in really fast. The zigzagging ball makes it easy to score a bunch of Foul Balls and unless you've upgraded the Power Stat, successful hits will often stay in the park because of the wonky ball momentum.
** TIGGER. He will throw the ball at you normally, but then IT BECOMES INVISIBLE. Yes, the ball is invisible. And you have to successfully score 28 homeruns out of 40 balls. That means you can only miss, hit, or foul 12 balls.
** Christopher. Freaking. Robin. You have to hit FORTY HOMERUNS out of FIFTY balls. Christopher Robin can use a combination of ALL of the strategies of the other characters, and will usually use Kanga and Roo's or Owl's technique. And he's capable of using invisible balls too. Oh he can throw balls normally too, but they're usually too fast for you to hit.
* Technically not a video game example, but Roleplay/DinoAttackRPG had a few infamous bosses that would certainly qualify:
** Cam O'Cozy- oh boy. Where to start here. The guy must have been defeated ''at least'' five or six times before he was finally killed off just because of how much he frustrated everyone. First he [[Film/DrStrangelove apparently fell to his death by riding a bomb]], then he returned as a BigBad plotting to murder anyone with the ''slightest'' idealistic beliefs. He was arrested by the cops but (without his creator's permission or involvement) he came back yet ''again'' on Adventurers' Island, and was finally given a [[spoiler:RoboticReveal]] that served to both get rid of him for good ''and'' justify his presence in the RPG to begin with.
*** Duke was practically TheDragon to Cam O'Cozy, and just as bad (if not worse). If not for popular demand he would have very easily escaped from a maximum security prison with relative ease.
** The Brickspiderbot: Simply ''fighting'' this thing practically took up an entire story arc (funnily the same arc with Cam O'Cozy and Duke).
* ''VideoGame/{{Warframe}}'':
** The dual boss fight with Captain Vor and Lieutenant Lech Kril on Phobos isn't that hard, as the bosses don't do much damage, but it is NOTORIOUS for glitching out and being impossible to beat. Have fun farming the Miter, Twin Gremlins, and Trinity!
** General Sargas Ruk can be a pain in the ass for new players. The first phase of the fight is pretty easy, all he does is spray fire at you, and you have to blow off his arm. The 2nd phase he gets a room clearing Supernova that's next to impossible to dodge and knocks you down, doing a huge chunk of damage, he also gains a missle attack in this form that will absolutely WRECK you if you get hit by it, and you WILL get hit by it. His 3rd phase cuts the bullshit and he gains an attack that launches Fire Pillars out of the ground underneath you similar to Ember's World on Fire, with the appropriate damage, standing still for more than 3 seconds with kill you unless you're playing as Rhino or another beefy frame.
* In [[PuyoPuyo Puyo Pop Fever]], normally you have to deal with Popoi at the end of a story route, who is already fairly challenging. However, if you do well enough on the hardest story route, you run into [[spoiler:Carbuncle]], who will outright BREAK you. Basically, his dropset gives him a ton of large Puyos-more than any other character in the game-making it easier for him to both set up large combos or offset repeatedly to trigger Fever. Couple this with a brutal AI that can set up 5 and 6 chains in the blink of an eye and is prone to immediately going into a [[LimitBreak 30-second Fever mode]] the moment you think you have him threatened and you have one of the nastiest single-player fights in the series.
* {{Pinball}} example: In Creator/SternPinball's ''Pinball/HighRollerCasino'', the Craps game comes across as this, as it has a difficult target to shoot, an open-ended number of shots to make, and can only be advanced during single-ball play.
* ''VideoGame/StreetPassMiiPlaza'': The final boss of ''Warrior's Way'', Emperor Fynalle. Every other battle up to him was a mix of properly dividing an army and TacticalRockPaperScissors. Fynalle, on the other hand, is a straight out five round game of Rock Paper Scissors against an army that starts out eight times your size. There's no strategy; it's a LuckBasedMission that requires either grinding for Play Coins or extreme luck in telling what he will do.
* In ''[[VideoGame/TonyHawkProSkater Tony Hawk's Underground]]'', it's the final skate-off with Eric Sparrow. He challenges you to a race across your hometown to regain a tape that had your ultimate stunt on it. To win it, you pretty much have to play Follow The Leader, hitting every marker while Eric drops... some sort of flames to mess you up. Oh, and you only have 3 minutes to do this. Thankfully, the game decides that once is enough and subsequent plays use a version which gives you a ''very'' satisfying TakeThatScrappy.
* ''Yoshi's Safari'' has two of these: Magikoopa and Big Boo. Magikoopa teleports rapidly all over the place, thus making it very hard to hit him. As soon as he fully reappears he'll immediately fire off a magic shot that takes several shots to destroy before immediately teleporting around again, only giving you a split-second to hit him. Between defending against his shots and shooting all around trying to catch him as he reappears, expect your power meter to be very low throughout the fight. As for Big Boo, what makes this fight so hard is the constant stream of debris flying toward you, and all while moving around chasing down a constantly-moving Big Boo with many invulnerability frames. After you take him down, he'll split into three smaller Boos, and you have to aim at the one with the tongue sticking out, still with the invulnerability frames and the flying debris. You'll most likely need your mushroom item for this fight.