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->''"Tyrant Overlord Baal? Wasn't he just a ploy to force players into playing their games for 100 hours longer?"''
-->-- '''Mao''', ''VideoGame/Disgaea3AbsenceOfJustice''

The Bonus Boss is one that often exists outside the normal plot of the game, and requires quite a bit of conscious effort to get to. Its difficulty is usually much beyond that of the "story line" final boss. Occasionally, games may have more than one Bonus Boss. The key point here is that they make up the most difficult enemies in the game, and that includes the actual last boss of the game. Sometimes, the player may acquire an InfinityPlusOneSword or ability once they beat this extraordinarily difficult enemy, but it's usually a BraggingRightsReward. Anyone who can beat the Bonus Boss has proved they don't need them, unless it's to get to another Bonus Boss even harder than the previous one.

A Bonus Boss can technically be a GiantSpaceFleaFromNowhere, but then again, ''you'' went looking for it.

Compare TrueFinalBoss, which is often (but not always) a BonusBoss that, when found or unlocked, ends up [[BaitAndSwitchBoss replacing]] or [[SequentialBoss coming right after]] the FinalBoss, requiring you to beat it in order to clear the game.

A BonusBoss that drops useful items may lead to UnstableEquilibrium. A BonusBoss that is a boss from a previous game is a LegacyBossBattle.

----
!!Examples:

[[foldercontrol]]

[[folder:Action Adventure Games]]
* The Four Sword Links in the ''VideoGame/TheLegendOfZeldaALinkToThePast'' port on the GameBoy Advance. Each Link had some abilities that Link could use, such as the Hurricane Spin, the Magic Cape, etc. Beating them was purely for bragging rights.
* The UpdatedRerelease of ''VideoGame/TheLegendOfZeldaLinksAwakening'' for Game Boy Color featured a BonusDungeon based on color. The boss of the dungeon wasn't more difficult than the other bosses, but you could only enter the dungeon if you knew the color of the stalfos' clothes at the entrance. There were also a number of color-based puzzles that would be frustratingly difficult if you managed to get in anyway.
* ''VideoGame/TheLegendOfZeldaSpiritTracks'' has [[spoiler:Dark Link]] at the end of [[BossRush Take Em All On]]'s Final Level.
* ''Franchise/{{Castlevania}}'' series:
** ''VideoGame/CastlevaniaOrderOfEcclesia'' gave you the option to fight the Chinese vampire, Jiang Shi, in the Large Cavern bonus dungeon. He's not very hard, though, seeing as how proper use of Melio Scutum and any slashing Glyph would easily reduce his 6000+ HP down to nothing. Though this boss is interesting in the fact that when he dies, a seal is placed on his face, but if you break it off with an attack, he comes back to life, allowing you to fight him again as many times as you want. Not worth the attribute points though (30, 60, or 120).
** Galamoth in ''VideoGame/CastlevaniaSymphonyOfTheNight'' has more HP than Dracula and hits really, really hard. Fortunately, you don't have to beat him to meet the Count. Beezlebub is also optional, as are a few other bosses in the inverted castle.
** Legion, Nuculais, and Golden Bones in ''VideoGame/CastlevaniaCurseOfDarkness''.
** The Whip's Memory, an image of Richter Belmont in ''VideoGame/CastlevaniaPortraitOfRuin'', is part of a ritual to unlock the [[InfinityPlusOneSword true power]] of a [[MagikarpPower weakened Vampire Killer whip]]. Unlike the rest of the game, you can only battle this boss with Jonathan. Thankfully, "dying" in this battle just boots you out of the battle with full HP and MP instead of yielding a Game Over.
** ''VideoGame/CastlevaniaLamentOfInnocence'' has The Forgotten One, a [[ColossusClimb giant]], [[{{Gorn}} skinless]] demon trapped in the [[IDontLikeTheSoundOfThatPlace Prison of Eternal Torture]], an area accessible when you open the HubLevel. (You still need a late-game artifact to fight him, but the area is open.) Everything about him is terrifying, and he's pretty difficult. [[spoiler:Unless you use the Ice Whip.]]
* ''VideoGame/IllusionOfGaia'' has Solid Arm, a boss originally from the first game in the series, ''VideoGame/SoulBlazer'', who's [[GuideDangIt only fightable]] if you [[GottaCatchThemAll collect all fifty Red Jewels]].
* ''VideoGame/{{Aquaria}}'' has a number of optional bosses, but many consider Simon Says to be the most interesting. He's well hidden, and you don't actually fight him -- instead you play, well, [[ExactlyWhatItSaysOnTheTin simon says]], with a very useful third cooking slot as your reward for playing well.
* ''VideoGame/{{Okami}}'' has the [[spoiler: Bandit Spiders and the Kusa Five]].
[[/folder]]

[[folder:Action Games]]
* ''VideoGame/MetroidOtherM'' has the Metroid series's first bonus boss. If you play the post-credits sequence for 100% and the extra ending, you have to butt heads with [[spoiler:Phantoon from ''Super Metroid'', who not only has new powers, but is also much scarier looking than before. It is worth noting that the Phantoon fight was intentionally left out of Hard Mode.]]
* ''VideoGame/CaveStory'' has G-CLONE, fightable in the removed Wind Fortress that was restored in the Steam and 3DS eShop versions as a bonus area.
[[/folder]]

[[folder:Beat Em Ups]]
* The Red Dragon features as a BonusBoss in both of the ''VideoGame/DungeonsAndDragons'' {{Beat Em Up}}s.
* Rodin from ''VideoGame/{{Bayonetta}}'' can be fought if the player buys a Platinum Ticket for 999,999 halos. He is revealed to be a former angel, and is more powerful than [[FinalBoss Jubileus]]. What? You say he just looks like [[BigBad Balder]] with a ScaryBlackMan makeover? Well, consider this: Balder didn't have [[GiantHandsOfDoom Wicked]] [[GiantFootOfStomping Weaves.]] Not only that, but regardless of what difficulty you've been playing on, the Rodin fight is automatically set to [[HarderThanHard Nonstop Infinite Climax]] difficulty. He can kill you in two or three punches at the start of the fight. You want that Rodin weapon? If you don't know about the phone cheat, [[NintendoHard good luck.]]
* In ''VideoGame/RiverCityRansom'' [[DualBoss Benny and Clyde]] are the only bosses that you don't have to defeat in order to access River City High School. Once inside, you can also skip Tex as well, since only Otis has to be defeated in order to fight the Dragon Twins, and then Slick, [[spoiler:who is actually Simon.]]
* Via ''VideoGame/AsurasWrath'' DLC, two Bonus Bosses that have nothing to do with the main game story are [[StreetFighter Ryu and Akuma]], who become Evil Ryu and Oni respectively.
* The doujin game ''{{Grief Syndrome}}'' has Oktavia von Seckendorff, an optional sixth witch who can be fought [[spoiler:at any point as long as Sayaka is dead.]] This already-difficult fight is made harder by the fact that [[spoiler:you can't use Sayaka, who is generally considered the best character, against her -- as anyone who's seen ''Anime/PuellaMagiMadokaMagica'' to the end knows, Oktavia is the result of Sayaka becoming a witch]].
[[/folder]]

[[folder:Fighting Games]]
* ''MortalKombat'' is the TropeMaker:
** [[VideoGame/MortalKombat the first game]] has Reptile as a secret boss. There is [[LuckBasedMission a very small chance]] that he will appear before the fight begins and give you clues on how to find him (ex."Look To La Luna"). You can only fight him if, on the fight at the Pit stage, you don't block, get a [[FlawlessVictory Double Flawless]] on your opponent, and finish them with a Fatality. Furthermore, [[LuckBasedMission there must be a ghost floating in front of the moon]]. If the conditions are met, the screen will flash with the words "You have found me, now prove yourself!" appearing, whereupon you will be taken to the Bottom of the Pit to fight him.
** ''VideoGame/MortalKombat2'' continued the tradition with Noob Saibot, Jade, and Smoke. Noob Saibot appears only if you win 50 battles consecutively. Jade appears if, on the fight before the question-mark box, you only use the Low Kick button to defeat your opponent (can be done on any round). Smoke is the most difficult to get, as you have to make Dan Forden appear and say "TOASTY!" while fighting on the Portal stage, then hitting Down + Start while he's on the screen.
** ''VideoGame/MortalKombat3'' had Smoke as a hidden boss via one of the 11 hidden treasures of Shao Kahn that you can access after beating the game, as well as Noob Saibot. ''Ultimate MortalKombat 3'' added Mileena, Ermac, Classic Sub-Zero, and Human Smoke. ''MortalKombat Trilogy'' added Chameleon and Khameleon, who were basically all the male and female ninjas rolled into one, respectively. You can also fight every single one of these characters via the Kombat Kode system.
* Akuma from the ''StreetFighter'' series is usually a bonus boss in the games where he isn't the TrueFinalBoss, particularly in ''[[{{Street Fighter II}} Super Street Fighter II Turbo]]'', ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha]]'', ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha 2]]'' (as Shin Akuma), and ''VideoGame/XMenChildrenOfTheAtom''. The former is notable in that even if you're playing as a character whose final boss is supposed to be Akuma (like Ryu or Gen), you will simply fight Shin Akuma first and then you'll face the regular version of him.
** The CPU version of Dan also served this role in the first ''VideoGame/StreetFighterAlpha'', as did Q in ''VideoGame/StreetFighterIII: 3rd Strike''.
** In ''[[VideoGame/StreetFighterAlpha Street Fighter Alpha 2]]'' and ''VideoGame/StreetFighterIII: 2nd Impact'', each character has a specific rival who can only be fought if the player manages to fulfill certain conditions without losing a single match.
* Baiken, in the original ''GuiltyGear'' for PS1. In order to get to her, you had to beat the game as Sol or Ky, without using any continues -- once you get to her, though, you can try to win as many times as you like, and if you do, you unlock her as a playable character. Considering the extreme difficulty of defeating Justice the first time, and the first game's broken instant-kill mechanics, this was quite a task beyond the calling of most casual players.
* ''VideoGame/FatalFury'':
** Geese Howard in ''Real Bout Special''. He dies in the first ''Real Bout'', only to come back as "Nightmare Geese" in ''Real Bout Special'' (it's implied that the Nightmare Geese battle takes place in the player character's mind, as Geese has an odd aura around his feet and enhanced powers).
** Much earlier in the series, ''FatalFury Special'' had a BonusBoss in [[VideoGame/ArtOfFighting Ryo Sakazaki]], who was the first seed in the long running franchise known as ''VideoGame/TheKingOfFighters''.
** Finally, Alfred Airhawk fills this role in ''Real Bout 2''.
* ''VideoGame/SuperSmashBros'':
** ''Melee'' has Giant Kirby, who appears in the fifth stage of Adventure Mode if the group of smaller Kirbies is beaten in 30 seconds or less. Giga Bowser also appears as a bonus boss if you clear Adventure Mode quickly enough; and while he fights exactly like Bowser, aside from being bigger and stronger, you can't grab Giga Bowser to throw him off the stage.
** In ''Brawl'', extra doors appear in three stages after you beat Tabuu; going inside them will pit you against Toon Link, Star Wolf, or Jigglypuff, depending on the level. However, you only have one chance to defeat them and their AI is much more aggressive than the characters you fought previously.
* ''SoulCalibur 3'' also has a bonus boss. The arcade and Tales Of Souls modes will almost always be fought against Zasalamel's demonic form, Abyss, but an even stronger opponent called Night Terror can be fought. Night Terror will replace Abyss if the player encounters and defeats Olcadan before arriving at the cathedral where the last few battles take place. Night Terror can also be fought in the 'Final Battle' mission of the game's challenge mode.
* The ''VideoGame/VirtualOn'' series has several of these, some exclusive to certain versions. In the first game, if you win all your battles by Time Over, you'll get a Warning message and then enter a special battle with Jaguarandi, a mutated version of Raiden that varies each time you fight it. When you first fight it, it's about the size of a Raiden or a Belgdor, and its color is the opposite color of your mech. If you continue against it, [[BaitAndSwitchBoss it changes to a miniature toy-sized version that is colored purple, and its armor weakens severely (so much so that a close range attack from Apharmd will kill it instantly), and if you continue again, it can be killed in 3 hits by Temjin's Beam Rifle!]] In the Japan-only PS2 version, if you beat all 8 virtuaroids in under 30 seconds, [[TrueFinalBoss you will hear a special chime and fight the original Fei-Yen instead of Z-Gradt]]. This version of Fei-Yen is always in Hyper Mode, but its armor is not weakened and its attacks are more powerful than the regular Fei-Yen.
** The sequel, ''Oratorio Tangram'', has Ajim -- a crystalline, transparent virtuaroid. To fight him, you must win at least one battle in your run with a Time Over. Once this is done, he will appear randomly at any time, even as late as the Raiden fight, [[DeathFromAbove crashing down on your opponent and destroying them]]. His stats are beyond mortal comprehension, meaning that he's faster and stronger than all other virtuaroids, and all damage done to it is lessened to roughly 5/8 of the usual. Oh, and you can't beat him via Time Over either -- if you try and do this, you will lose automatically. Encountering him automatically unlocks him for regular play in the later revisions, but on the Dreamcast version 5.45, he was only playable by beating him, then beating the game, and holding both Turbo buttons on the Random select box on the latter half of each month. And when you play as him, he has the weakest armor in the game, and to make matters worse, his health drains by 2% every second.
*** ''FORCE'', the 3rd installment, has Shadow versions of your team that you can fight by, once again, getting Time Overs. These Shadow mechs are manifestations of a virus in the system, taking the forms of your mechs and making them much stronger than the normal version. Jaguarandi also returns, but as the default mid-boss, and this time it becomes '''LUDICROUSLY HUGE''', taking up over half of the arena. It's also a mutated Guarayakha now instead of a Raiden, trading in most of its long range advantages for godlike close range combat tactics. Ajim also appears, with a female version of it called Guerlain, but as the final boss, and utilizing completely different moves than before.
* ''Galaxy Fight'' and ''VideoGame/WakuWaku7'', the two fighting games made by Creator/{{Sunsoft}} for the NeoGeo, shared a common bonus boss named "Bonus-Kun", a punching bag (from "[[PlanetOfHats the Punching Bag Planet]]") with a limited moveset who parodies [[StreetFighter Ryu]]. In ''Galaxy Fight'', [[DidYouJustPunchOutCthulhu after you defeat Felden]], you get to fight a final BonusBoss in the form of Rouwe, an old man dressed in a karate gi.
* ''VideoGame/SamuraiShodown 2'' had a very tough BonusBoss in Kuroko, whom you could either fight by meeting certain conditions, or just randomly after stage 3.
* ''OneMustFall'' has a few.
** In the One Player story mode, there's Fire and Ice. To take on Fire, you need to be playing on at least the hardest non-hidden difficulty, beat your opponent on the Fire Pit arena, do a destruction on them, and enter a robot-specific code. If playing on the very hardest difficulty, beat Fire and do the destruction and code again and you can fight Ice. These two are extremely hard to beat, but the devs reward you generously for doing so. Normally, the end of round bonuses on the hardest difficulty are 400,000 points. For Fire, they're 2 million points, and for Ice they're 20 million points. Good luck getting a perfect round against Ice. The only way to not take any damage from him is to not take any hits ''at all'', as he can still damage you even when blocking.
** In the tournament mode, there are various unranked challengers in each tournament. All of them are hard, and most require you to be playing on the hardest difficulty. If they're going to show up, they'll challenge you after doing a destruction on some other opponent. There's at least one occasion when one unranked challenger will challenge you after beating another unranked challenger, too.
* ''VideoGame/BloodStorm'' had several of these, all of them {{Palette Swap}}s of your main characters. Unlocking most of them was both fun and [[GuideDangIt ridiculously frustrating.]] For example, one of them required you to knock down a stalactite in one stage using projectiles, so that it falls down a pit. Then, you have to jump down, land on the small platform, and then you'll be able to fight the boss. Another required you to drop your weapon, and then perform the "pick up" command so that you touch the center of a summoning circle. And so on.
* The final boss of the story mode in ''VideoGame/DissidiaFinalFantasy'' is Chaos, who is only level 50 or so and thus can be defeated easily with LevelGrinding. However, beating him opens an extra campaign whose final boss is a level 110 Chaos called Ultimate Chaos.
** Duodecim does the same thing, replacing the more-than-max-level Chaos with Chaos' new more-than-max-level OneWingedAngel, Feral Chaos. Your reward for beating him? The ability to play him.
* Tekken 2 has Roger the kangaroo, who appears in the fourth stage if you beat the third stage with low enough health to get a "Great!" from the announcer. Beating him and the rest of Arcade Mode will unlock him and his MovesetClone Alex, who is a dinosaur.
* In ''VideoGame/{{Tekken}} 6'', there's Nancy. She's basically one of several [[HumongousMecha giant robots]] developed by the Mishima Zaibatsu, perhaps to combat [[BigBad Azazel]], who [[MightyMorphinPowerRangers is finally free after 10,000 years.]] Her appearance is sort of a BigLippedAlligatorMoment in that you get rewards for beating her but if you don't, it has absolutely no bearing on your progress and you don't get the option of fighting her again without restarting. [[spoiler:She is playable, but only in one level of Scenario Campaign.]]
* ''VideoGame/LightningLegendDaigoNoDaibouken'' has two of them, Girigiri Oyaji (the game's MrExposition and sponsor of the AllThereInTheManual national fighting tournament) and K.O.J. (the current champion of said tournament). You'll fight them after the FinalBoss, if you have finished the game with all regular characters, then did a NoContinueRun (and for K.O.J., you need on top of that to gather one hour's worth of matches) beforehand.
* In ''VideoGame/BlazBlue'' the only way to fight Unlimited Ragna is to go through [[NintendoHard Score Attack Mode]] or to play through arcade mode finishing each opponent with a Distortion Drive.
** ''[[VideoGame/BlazBlueContinuumShift Continuum Shift: Extend]]'' features "Abyss Mode", where a special version of Unlimited Ragna appears at [[NumberOfTheBeast Depth 666]]. The first thing you'll notice is that he'll already be across the screen in a few short frames, making him more annoying to fight than Taokaka in terms of speed.
* In ''VideoGame/Persona4Arena'', it's possible to unlock a special bonus match against [[spoiler:Elizabeth, from VideoGame/{{Persona 3}} (see below)]]. She is an SNK Boss to the core, can inflict multiple status effects, can heal herself, and is ''insanely difficult to defeat''. If she is in a position where she can win the match, she'll just perform her OneHitKill attack on you and be done with it.
* Vampire Savior has Oboro Bishamon, the man himself, rather than the armor. VideoGame/{{Darkstalkers}} 3 makes him playable.
[[/folder]]

[[folder:First-Person Shooter ]]
* ''VideoGame/{{Borderlands}}'' has some in the optional side quests, some of which, like Mothrakk and Marley & Moe, can reach ThatOneBoss status.
** The ''true'' BonusBoss doesn't come until you've downloaded and finished ''The Secret Armory of General Knoxx''. That unlocks a fight against Crawmerax the Invincible, which is pretty much ExactlyWhatItSaysOnTheTin. In case it's not clear, the game spells it out for you: the quest where you have to fight him is called '''"You. Will. Die."''' And the road leading to Crawmerax's lair features a road sign saying "[[LampshadeHanging Secret Final Boss]]".
* ''VideoGame/{{Borderlands 2}}'' keeps it up with a ''number'' of such enemies, with each DLC featuring a new Raid Boss:
** Terramorphous The Invincible, who is even ''worse'' than Crawmerax. To quote a dev: "If you don't die at least 5 times before killing him, then we haven't done our jobs." The name of his quest? '''[[ContinuityNod "You. Will. Die. (seriously)"]]'''
** Some enemies can evolve in-game to turn into more powerful and resistant (and fully healed) versions of themselves. Most of these are still manageable. Let an Ultimate Badass Varkid evolve? You get [[NamesToRunAwayFromReallyFast Vernivorous The Invincible]].
** Hyperius the Invincible, a mutated, power-mad Hyperion engineer found in the ''Captain Scarlett and Her Pirate's Booty'' DLC.
** Master Gee the Invincible, a PuzzleBoss from the same DLC, and his horde of sand worms ([[DangerouslyGenreSavvy who will avoid the player if they're in Fight For Your Life]]).
** ''Mister Torgue's Campaign of Carnage'' gives us Pete the Invincible -- Pyro Pete isn't a very impressive boss when you fight him the first time, but when Moxxi says he's been working out since then, ''she means it''.
** ''Sir Hammerlock's Big Game Hunt'' has Voracidous the Invincible, who is aided by a powerful Witch Doctor who will buff Voracidous with his shields once killed.
** ''Tiny Tina's Assault on Dragon Keep'' has The Ancient Dragons of Destruction, a WolfpackBoss consisting of four dragons, two of which are capable of leveling up the other dragons and healing.
[[/folder]]

[[folder:Hack and Slash]]
* ''Diablo II'' has some in its later updates. Versions 1.00-1.09 had the Cow King as a sort of Bonus Boss, though he was substantially weaker than the actual final bosses. Version 1.10 introduced Uber Diablo as a new Bonus Boss, and 1.11 introduced the Pandemonium Quest, which involves looking for keys and battling buffed-up "Uber" versions of bosses (Uber Izual, Uber Duriel, and an important lore character Lilith, who is basically a "Uber" version of boss Andariel). The result of the quest is players entering the Uber Tristram, where they must fight an epic battle against Uber Baal, Uber Mephisto, and Pandemonium Diablo, the super versions of the three prime evils, who attack all at once!
* ''Diablo III'' has the Infernal Machine update, which introduces four unique bosses, the key keepers, in each act. After obtaining all the keys, the player could craft the Infernal Machine, which allows battling two super-versions of game's bosses at once, for great rewards. There are three such battles: Maghda and the Skeleton King, Ghom and Rakanoth, Zoltun Kulle and the Siege Breaker Assault Beast. There is a special reward for winning all three battles and collecting special rare items from them.
* ''Dungeon Siege'' has two. One is easy to find, while the second is extremely hard. The first is Scorch, the ancient dragon of Rathe, whom the player could avoid simply by continuing by the road to Castle Ehb. Scorch is the biggest monster in the game, has the highest number of HP, and is nearly as deadly as the final boss. The second Bonus Boss is located in the hard-to-find secret "Chicken level", amongst the various chickens named after the game's developers. It is [[spoiler:Colonel Norick, the boss version of the first NPC quest giver in the main game, an old man who dies in front of the player. He also is a spoof on Colonel Sanders of KFC fame]].
* In the {{sequel}} to ''VideoGame/OtogiMythOfDemons'', the last bonus mission in the Forest of Havoc is a duel with The Crimson King, a recurring character from the first game. How hard is he? Let's list the ways. He hits like an angry truck, he can move just as fast as you, he throws magic fireballs that cause a bad status effect, and his ultimate attack hurts like hell... did I mention that it's a HomingProjectile? If you had trouble beating the last boss of the game, then The Crimson King will wreck you without mercy.
[[/folder]]

[[folder:[=MMORPGs=]]]
* Most MMO[=RPGs=] have such things: Giant Monsters in ''VideoGame/CityOfHeroes'', world/raid bosses in Everquest, and raid bosses in ''VideoGame/WorldOfWarcraft''. Some are 'storyline' bosses, of course, but a lot of them are easily skippable.
* ''GuildWars'' features a few of them, most notably Urgoz, Kannaxi, Mallyx, Duncan the Black, and, most recently, Dhuum. To make matters worse, all of them (save for perhaps Duncan) have a hard dungeon to finish in one sitting before you can face them; if you die, you have to do it all over again! The placement of Mallyx and Duncan make them candidates for TrueFinalBoss.
* ''[[GaiaOnline zOMG]]'' features the Landshark, which appears semi-randomly in Gold Beach. The Landshark is one of the only charge level 10 (max CL) monsters in the game, and features insane attack power, extremely high HP, and attacks that can take up almost the entire screen. If you see one, running is advised.
** A recent update nerfed the Landshark to more manageable levels. (It's now only CL 7). However, a gamut of new bonus bosses were added in its stead, as well as "Challenge" versions of all Instance Bosses. While none of these (with the exception of [[spoiler:Sea Witch and Labtech X]]) are CL 10, they have the added difficulty of only being vulnerable to individuals below a certain charge level. Meaning that players wishing to battle Airshark need to suppress their CL to level ''2''.
* ''VideoGame/WorldOfWarcraft'' also has its share of bonus bosses. The first one was Nightbane in Karazhan, where the only way to access him was to complete a certain quest chain. ''Wrath of the Lich King'' also introduced bonus bosses in some of the regular dungeons that are only accessible on Heroic difficulty. However, the [=WotLK=] bonus bosses tend to be much easier than the the FinalBoss of their respective dungeons.
** Just in case that isn't enough (likely, given how hardcore some fans of the game can be), many of these same bosses have special conditions that can be attained for Achievements (a BraggingRightsReward, since you can't do anything with the points you accumulate from achievements), which often turn fairly normal bosses into insanity. For example, one of these takes place in a dungeon where there are minibosses that you can kill to make the main boss easier; for the achievements, you have to leave at least one of the minibosses alive until you engage the main boss. For the hardest achievement, all three get to stay up, and ''they come help the main boss while you're fighting him''.
*** Yogg-Saron, the final boss of [[TailorMadePrison Ulduar]], has a similar hard mode: you are required to defeat his four jailers, the Watchers (whom he's driven mad; defeating them restores their sanity) in order to open the path to Yogg's chamber. If you ask, they'll help you in the fight against Yogg-Saron. The achievements for defeating Yogg-Saron take the form "X Lights in the Darkness", where X is the number of jailers you ask to help you. Asking ''none'' of the jailers to help you is referred to as "Yogg+0", and is -- even two updates later -- the hardest fight in the game.
** The Temple of Atal'Hakkar (aka Sunken Temple) has the first bonus boss in the game: The Avatar of Hakkar. You need to complete a quest chain to access him, too, and he's actually harder than the dungeon's final boss, Eranikus the Dreamer.
** The best example, however, is Algalon the Observer (a.k.a. [[FanNickname Algalon the Raid Destroyer]]) in the Ulduar raid. He is only accessible if you complete a quest that requires the player to kill several bosses in [[HarderThanHard hard mode]], and if he's not killed within an hour or so from summoning him, he'll despawn and you have to wait till the raid reset to summon him again. Algalon was ''not'' the hardest boss in the game when he was released -- that honor went with Yogg-Saron on full [[NintendoHard hard mode]] (see above) -- but he was the one that the fewest raids defeated, between the difficulty of the path to get to him and the difficulty of the fight itself. (As a special bonus, story-wise, if you fail to defeat Algalon, he sends a signal to ''his'' superiors to begin [[TheEndOfTheWorldAsWeKnowIt sterilizing the planet to rid it of corruption so that life can begin anew]]. Also, in-story, [[spoiler:it's stated that he could completely and utterly ''[[CurbStompBattle wreck]]'' Yogg-Saron in a fight, and the main thing keeping him from actually doing so is that it would [[ApocalypseHow annihilate the universe]]]].)
** Jin'do the Hexer in Zul'Gurub was optional; you can actually skip him, and he drops some of the best loot in the dungeon next to Hakkar. Two other bosses were accessible through skill-related means; it was possible to fish up Gahr'zahka by catching fish to make a lure for him, and preparing a certain kind of mojo with Alchemy enabled raids to fight bosses at the Edge of Madness.
*** In the re-released Level 85 Heroic Zul'Gurub, people with enough Archaeology skill can access the optional boss at the Edge of Madness.
** The Bug trio, Viscidus, and Ouro were all optional bosses in Temple of Ahn'Qiraj. Most, if not all guilds, did the Bug trio because the fight wasn't very difficult and it rewarded good loot. Viscidus is a fight that many guilds skipped because, even at level 80, it's still [[PuzzleBoss a pain]] in the ass. To defeat Viscidus, he must be frozen; naturally, he can only be frozen by Frost-based attacks, such as Mages' Frostbolt or Shamans' Frost Shock. Once Viscidus is frozen, then everyone in the raid must melee him (yes, even the healers need to). If melee'd enough times, he will shatter. All while attempting to freeze and shatter Viscidus, the raid must survive near-constant [=AoE=] Poison damage. Ouro is a fight that most Alliance guilds would skip in favor of C'Thun because A) he offered better loot and B) killing C'Thun at 60 was a significant achievement for raiding guilds. (Horde guilds would run him over due to Poison Cleansing Totem.)
** A number of dungeons from ''Wrath of the Lich King'' have a boss that only appears when running the dungeon in Heroic mode. Eck in Gundrak is a good example, as not only does he only appear on heroic, but also appears in a side alcove that opens up after Moorabi is defeated on Heroic.
** Recently introduced with the ''Cataclysm'' expansion is Lady Sinestra. Only accessible in 10 and 25 man raids, AFTER clearing the entirety of the Bastion of Twilight in Heroic mode.
** In the Firelands, Ragnaros has an entirely new fourth phase on Heroic mode.
** In Mists of Pandaria Patch 5.2, there is a bonus boss at the end of the Throne of Thunder raid, Ra-den. He is only accessible after you have defeated the previous 12 bosses. On ''heroic mode''. Oh, and you know nothing about how to defeat him. Have fun!
* ''CityOfHeroes'' has the Army of Me badge, unlocked via a special option in a Villain Side story arc. The mission? [[OneManArmy Beat a full team]] [[CloningBlues of yourself]].
--> ''You don't understand the math behind it, but you're pretty sure you're equal to or greater than eight of yourself.''
* VideoGame/FinalFantasyXI has the Notorious Monsters. The most, well, notorious of these are the Pandaemonium Warden, a SequentialBoss [[UpToEleven with 10 different forms]] who has to be beaten in 2 hours[[note]]the time limit was instated after a group battled him for ''[[MarathonBoss eighteen hours straight]]'' and ''still'' didn't win[[/note]], and Absolute Virtue, who was originally designed as a HopelessBossFight. Allegedly, they revamped him to be beatable, but other than exploiting bugs, nobody has yet beaten him. That's right: in an online game with over a million players, no group has even once managed to overcome Absolute Virtue.
** He has now been beaten legitimately. It happened within two months of the Level Cap being raised to 80, but he is still nearly impossible.
*** He was beaten legitimately before by an alliance of Scholars stacking Modus Veritas, cue Modus Veritas getting a monster nerf to the point it's a waste of time and merits.
* KingdomOfLoathing has the final bosses of the Clan Dungeons, and the three final bosses of The Sea.
** Mother Slime in the Slime Tube, who can be up to level 8700. She can also gain immunities to elemental damage and is immune to stunning moves and items.
** The Necbromancer in the Haunted Sorority House, who has three forms and a special attack that takes 30% of your HP.
** Hodgman the Hoboverlord in Hobopolis, who has 25000 HP, gains buffs depending on whether his [[TheDragon dragons]] are defeated or not, and is one of the few enemies that can flip out unprovoked. Defeating him earns you one of many powerful items, but the strongest, his Imaginary Hamster, requires [[SpeedRun getting to him in one day and in under 1100 turns]]. Due to the timing involved, this means [[HarderThanHard not killing any of his lieutenants]].
** Dreadsylvania has two possible bosses for each of the three zones: the Dreadsylvania Woods ends with either Falls-From-Sky, a [[EldritchAbomination bugbear made of stars]] that hits with a variety of powerful elemental attacks, or [[PunnyName the Great Wolf]] [[{{Airwolf}} of the Air]], a hard-hitting winged werewolf; the Dreadsylvania Village has either Mayor Ghost, who randomly prevents you from dealing elemental damage, using spells or skills, or using combat items in the next round, or the Zombie Homeowner's Association, which is virtually immune to abilities that don't do extra damage to group monsters; finally, the Dreadsylvania Castle ends with either the Unkillable Skeleton, who scales to your stats, prevents use of combat items, and is only vulnerable to physical damage, or Count Drunkula, who takes drastically less damage unless your character is severely inebriated, and must be defeated in ten rounds.
*** [[http://kol.coldfront.net/thekolwiki/index.php/Advanced_Dreadsylvania_Mechanics#Bosses_and_Superbosses There exist Hard Mode versions of the Dreadsylvania bosses]], which are even ''more'' dangerous but drop even better loot. [[GuideDangIt Good luck finding them without a guide.]]
** [[BonusDungeon The Sea]], meanwhile, has bosses that are even tougher than the Clan Dungeon bosses, matched only by the Hard Mode Dreadsylvania bosses:
*** Shub-Jigguwat, Elder God of Violence, who saps all your MP (and some of your HP) at the start of combat, is immune to stuns, and is virtually immune to elemental damage. He will also retaliate fiercely if you hit him with anything but a basic attack.
*** Yog-Urt, Elder Goddess of Hatred, who sticks you with an effect that lasts about eight rounds, caps all your stats around 30, prevents you from using skills, does massive damage to you each round, ''and'' prevents you from attacking her on pain of death. She's also immune to stuns and won't let you use the same item twice in one combat.
*** [[spoiler:Dad Sea Monkee]], who can only be faced in the first place if you beat both of the first two Sea bosses as ''all six character classes'', combine their special drops into six pieces of equipment, and wear them all. He's immune to being stunned, prevents you from using combat items, and is vulnerable to only one of the six types of damage each turn (including physical and all five elements). The order of those vulnerabilities is [[GuideDangIt only vaguely hinted at in the cryptic, unsettling message you get before facing him.]] On top of all that, you have twelve rounds to defeat him before you lose the fight automatically.
* ''DragonNest'' has several high level maps feature alternative routes with different bosses.
* There are two in ''StarWarsTheOldRepublic'':
** The Dreadful Entity. To summon the Entity at all, Dreadtooth, the world boss of Section X, must be defeated with full stacks of Dreadful Resurgence. The fight is quite a task, almost demanding a full operation's group. To add to it, Dreadtooth only gains stacks as he is defeated. Upon spawning, he starts with two. When he spawns again, he has four and so on. If Dreadtooth is defeated, he drops a special amulet which can be used to summon the Entity during the "Terror From Beyond" operation. But only in 16-player Hard Mode. To add to this, he has a special ability, Dread Touch, which is mitigated by another item: the Dread Guard's Corrupted Mask.
** Upon Dreadful Entity's defeat, the Dreadful Entity drops an item called the Dreadful Orb. This is used to summon the second bonus boss - The Hateful Entity, in the Scum and Villiany operation on 16-player Nightmare Mode. Boasting the same abilities as Dreadful, but hitting much harder and requiring very specific kiting tactics to defeat, the sight of players with his unique title are rare indeed.

[[/folder]]

[[folder:Platform Games]]
* ''VideoGame/MegaManX6'' had some bonus bosses by going through alternate routes to fight Zero Nightmare, which nets you Zero, and High Max, which lets you skip straight to the last areas of the game, although it's hard to find out [[GuideDangIt how the hell you're supposed to even damage him.]] (Hint: [[spoiler:Stun him with a charge shot, then hit him with any special weapon]].) Going to the secret areas again will let you fight Dynamo, which lets you get large amounts of souls.
** ''X8'' had Cut Man, again. You need to go through Optic Sunflower's stage to reach a 3D-ified version of where you fought him in Mega Man.
** ''[[VideoGame/MegaManX3 X3]]'' had Vile MK-2, which does nothing when defeated, except when his weakness (Ray Splasher or Spinning Blade) is used to score the final hit, in which case you won't fight him later. This is only the first step in getting the InfinityPlusOneSword. There was also Bit and Byte, who, like the X-Hunter example below, you could find and battle in hidden areas in stages. If you beat them using their weaknesses to score the final hit (Frost Shield or Triad Thunder for Bit and Tornado Fang or Ray Splasher for Byte), then they would be replaced in the final stage by Press Disposer. If even one of them was left alive, however, then the player would fight Godkarmachine O Inary in the final stage. Also, if Vile was defeated, the player would fight Volt Kurageil and Mosquitus in the final stage instead - defeating Mosquitus with Zero is the requirement for X to obtain the Z-Saber.
** ''[[VideoGame/MegaManX2 X2]] has the X-Hunters, Serges, Violen, and Agile, who can be encountered in hidden areas in stages. If you beat them at the first opportunity, you receive parts of Zero, and collecting all of them enables you to skip the fight with Zero in the final stage. You still fight the X-Hunters in the final stages, regardless of whether you fought them before or not, though.
* In ''VideoGame/MegaManZero 3'', in a secret area in the second-to-last level that can only be opened by going into {{cyberspace}}, Zero will encounter Phantom, who died two games earlier, ready to fight him to [[SecretTestOfCharacter test his worth as a hero]]. Victory will net the player the [[InfinityPlusOneSword infinity plus one, er, boots]].
* ''VideoGame/MegaManClassic'':
** Proto Man in ''VideoGame/MegaMan7'', who can be fought in a secret area in Shade Man's level after meeting certain requirements. The reward is his shield.
** ''VideoGame/MegaMan8'' had two in the SegaSaturn version, and they happen to be Cut Man and Wood Man from ''VideoGame/MegaMan1'' and ''[[VideoGame/MegaMan2 2]]'', respectively. Unlike their original appearance, however, they only give you bolts to buy weapons with. Cut Man is hidden in Duo's stage halfway through the game. Wood Man doesn't play the trope straight, though, as you fight him right before the continue point in Search Man's stage.
** ''VideoGame/MegaMan10'' gives you the option to buy three extra bosses as DownloadableContent. They show up only in TimeTrial mode, though, but they give Mega Man three very useful weapons only he can use.
** [[GameMod ROM hack]] ''VideoGame/Rockman4MinusInfinity'' has Crash Man and Wave Man. Finding their secret locations and beating them allowed Mega Man to use the Wire and Balloon Adapters before the Cossack Castle stages.
*** Also, doing a NoDamageRun through the entire game (up to and including the first two Chimerabots) has [[spoiler:[[RecurringBoss Shadow Man]]]] replacing the third and final one [[spoiler:by way of DiagonalCut]].
** Fan game ''VideoGame/MegaManUnlimited'' has Yoku Man. You unlock his stage by collecting 4 letters hidden in alternate paths of four of the eight Robot Master stages, and killing him gives you the Yoku Attack, which is a homing attack that can also be used to grab out-of-reach items [[spoiler:and also [[HoistByHisOwnPetard kill Yoku Man in two hits]] in the BossRush later on]].
* In ''VideoGame/MegaManZX'', after beating the penultimate stage, a new area behind it opens up. Inside, past a path lined with the familiar disappearing blocks and spikes, you can find [[spoiler:Omega Zero, from the last battle in ''Zero 3'', complete with famous quote.]] This battle is noteworthy for actually being HARD, not just "OMG he's level 500", since this time your character has far fewer abilities. [[spoiler:Omega]]'s AI has also become much more aggressive since the last game, and can defeat you in literally seconds if you're not quick with the fingers. Beating him gives you [[spoiler:Model OX, who is -- you guessed it, Omega Zero, complete with a crapload of awesome special moves and total badassery.]] [[BraggingRightsReward Only not really, since you only get it after beating the game]] and it's not really that much better then Model ZX.
** If you have ''Zero 3'' and ''Zero 4'', you can fight four bosses from each in the same area. Beating all eight gives you the same reward.
* ''RatchetAndClankFutureACrackInTime'' has [[spoiler:Vorselon, Ratchet's father.....'s accountant.]]
** And also in ''RatchetAndClankGoingCommando'', there's a secret boss in Oozla, the Swamp Monster II. It's harder than most other bosses in the game and also rewards you with the Box Breaker after killing it. You can also only get there if you have the Gravity Boots, which you get much later on in the game. You will also probably need the game's most powerful weapons to defeat it.
* ''VideoGame/DynamiteHeaddy'' has a BonusBoss called "The Money" that is unlockable with a password you get by beating the bonus game four times.
* ''VideoGame/{{La-Mulana}}'' 's infamous [[BonusLevelOfHell Hell Temple]] has its own guardian, The Boss (no, not [[VideoGame/MetalGearSolid3 that one]]), a giant blob with Naramura's (the game ideator) signature face that [[ShoutOut behaves a lot like the 4th boss of ''Maze Of Galious'']] and summons smaller copies of himself that throw grenades around. Interestingly enough, The Boss is generally easy compared to the level around him.
* ''TheLegendOfSpyro: Dawn of the Dragon'' has Elite Enemies in every chapter. They look like [[PaletteSwap normal enemies with a few modifications.]] [[BossInMookClothing They're not.]] They're hard to ''damage,'' let alone kill...
* ''VideoGame/KirbysReturnToDreamLand'' has a BonusBoss that is exclusive to the BossRush mode called "The True Arena". [[spoiler:It's Galacta Knight, the popular FinalBoss of the Meta Knightmare Ultra mode of ''Kirby Super Star Ultra''.]]
** Also, there's a boss in Extra Mode that doesn't appear in the regular mode. [[spoiler:Remember that robot from the trailer for the Gamecube Kirby game that became this game? It's the HR-D3, the robot from the end of ''Kirby's Dream Course'' that was upgraded with abilities the HR-H from ''Kirby 64'' used. The Metal General EX found it, changed the logo on the front, and used it as a backup in case he was defeated in battle.]]
* ''VideoGame/MarioGivesUp'': Returning to "Area of Bonuses" after pressing all four switches allows you to reach [[spoiler:the Key Boss]].
* ''VideoGame/WarioLandSuperMarioLand3'' has Hinyari, located in [[SlippySlideyIceLand Sherbet Land.]] Amusingly, you can just walk right out of the battlefield through a convienently-placed door.
* ''VideoGame/SonicTheHedgehog2'' contains one only found in an updated re-release on iPhone/Android. It's still Robotnik/Eggman, this time dropping spiked balls which need to be under him when they fire back up in order to get him into range. [[spoiler:To find it, you need to fall down a bottomless pit in Mystic Cave, a pit which in every other version of the game is a very deep spike pit.]]
[[/folder]]

[[folder:Puzzle Games]]
* In ''Franchise/ProfessorLayton and the Unwound Future'', if you go to the Secret Content and submit a code saved from the second game, you get to do a bonus puzzle designed around the MacGuffin of the second game, and apparently designed by the second game's villain. It's an incredibly hard puzzle, and the villain refuses to let you use Hint Coins, as he wants you to beat this puzzle in its purest form.
** All three games in the DS series have a series of puzzles that are unlocked by way of completing the various side quests (for example, completing the mechanical dog in the first game or all the toy car courses in the third). Completing all those puzzles unlocks a final set of puzzles that are the most difficult in the game.
* The Archivist in ''{{DROD}} RPG: Tendry's Tale''. You get a special ending for beating him, which was meant to require [[TooAwesomeToUse saving up]] the [[OneHitKill Hand Bomb]] to use on him. The developers didn't actually know whether or not it was possible to get stats high enough to defeat him by normal combat. (It is.)
[[/folder]]

[[folder:Racing Games]]
* In any version of ''VideoGame/InitialDArcadeStage'', defeating every opponent in Legend Of The Streets mode will take you to a free battle with Bunta Fujiwara. He is extremely difficult to beat, often sporting RubberBandAI. Whether or not you defeat him, the credits will roll afterwards.
[[/folder]]

[[folder:Real-Time Strategy]]
* The Smokey Progg in ''{{Pikmin}}'' is one of these, as you have to go out of your way to find it and it drops an object that produces 100 Pikmin when it dies. It has the difficulty to match as well: just touching its slime trail can kill several Pikmin at once, and any Pikmin attacking the Progg will probably be thrown right into it.
* The enemy fountain from ''DefenseOfTheAncients''. It will fuck up anyone who goes in unprepared, and [[InstantWinCondition its destruction is completely unnecessary]].
* ''DawnOfWar II'' has two optional missions. One, against the Eldar, has you fight an [[PhysicalGod Avatar of their war god]], which is considered to [[ThatOneLevel the hardest mission the the game]], not just because the avatar is really strong, but because the damn thing calls in lots of vehicles for help. The other has you fight an [[AssKickingEqualsAuthority Ork Warboss]], who, while weaker then the Avatar, is still considered tougher than the final boss, though part of that is clearing either of the levels gives you a nice set of Terminator armor and because in the final level, you get to use your entire squad, unlike the rest of the game.
[[/folder]]

[[folder:Rhythm Games]]
* ''GuitarHero'':
** [[http://www.youtube.com/watch?v=W4M7f4-bhbE This bonus level from Guitar Hero III]], featuring Music/DragonForce's "Through The Fire And Flames", may be harder to beat than any of the above examples.
** There's also its predecessor: "[[http://www.youtube.com/watch?v=H8Xb5XyY5cE Jordan]]" from ''GuitarHero II''.
** And its spiritual successor "Visions" from ''Rock Band 2'', utterly punishing on both [[http://www.youtube.com/watch?v=DJralxgefcE guitar]] and [[http://www.youtube.com/watch?v=RoHWwrTeYLY drums]].
* From ''{{DJMAX}}'' Technika:
** In the Specialist set, getting 70% accuracy or lower nets you [[http://www.youtube.com/watch?v=FBwWIvq4jIU Fermion SP]], a chart riddled with ''FakeDifficulty'' due to sensor bugs when dealing with repeat (purple) notes. What's also agonizing about this is that if you're good enough to even unlock the set (via Special Set 6, where you need to pass the dreaded [[http://www.youtube.com/watch?v=OJkqyQT6AsY Son of Sun SP]]), you'll probably have to intentionally ''DoWellButNotPerfect'' to unlock Fermion SP, so getting there in the first place will leave your HP at a very, very bad value.
** In the Conqueror set, there will be a small chance that, instead of the usual boss charts, you'll get [[http://www.youtube.com/watch?v=Zdc4e1_u3Bo Thor TP]]; given that getting this song is excruciatingly random (or perhaps just insanely difficult, considering the theory that you'll have to get EXACTLY 98% or 94% accuracy), one does not have many chances to practice this song and will have to rely on Website/YouTube videos. A hacked mission in Platinum Crew (in celebration of the Mid-Autumn Festival) spat up [[http://i270.photobucket.com/albums/jj81/hiyorigawa/647.jpg a chance to practice it constantly]] until it was removed, presumably after Pentavision's warning to the Chinese [=PlatCrew=] management.
** In Technika 2, the Super Speed set brings us [[http://www.youtube.com/watch?v=A_QVFGjiWvg D2]], a song running at 356 BPM (approximately 1.5 times faster than Son of Sun)... not to mention that to unlock this song, you'll have to play a very, very buggy song called [[http://www.youtube.com/watch?v=cdSk3Ofhvww BEE-U-TIFUL]], whose difficulty comes from a painfully brutal segment featuring pinks that follow the melody and syncopated repeaters. This song is very likely to leave you in a worse state than if you had tried to unlock Fermion SP in Technika 1.
** This applies to all Club Mixing sets in general from the second game onwards, really, with the change in mechanics and criteria on how to reach a boss in a set. Whereas in the first game the boss is determined by the number of [=MAXes=] you've accrued during the set, now the boss you play depends on the difficulty of the set you've chosen.
** Notable examples from ''Technika 3'':
*** The high boss of the Sound Lab set is a 2011 rendition of Supersonic by the Pentavision Sound Team. Break! MX is a mandatory song to reach Supersonic. As of writing, Sound Lab is the only way that Supersonic 2011 can be played, outside of the Summer Special Mission last year.
*** Hyper Speed's high boss is Bamboo on Bamboo MX. The mandatory songs to reach BOB are Now a NEW Day MX and Right Back MX. While not as fast as the other songs in the set, NAND is still troublesome due to the hold note management present throughout. Right Back has one of the messiest new MX charts, as most of the notes tend to overlap with one another. Add to the fact that the screen must register your finger being lifted off, and you'll find yourself accruing Breaks and Misses back and forth.
*** Fatality, one of the most difficult disc sets along with T2's Maximum set, features a high boss in the form of Xeus MX, which is Thor on steroids, thus in the same league as D2 and Cypher Gate in difficulty. Like other Maniac performance sets, the prerequisite involves playing two specific songs. In this case, they are AD 2222 and Angel. Like other similar charts, Angel's MX chart is designed to push players beyond human capabilities, with (glitch-laden) tiring repeaters being its primary challenge. Many consider this to be HARDER than Fatality's Low Boss (Supernova).
*** Xeus during the first few weeks after the release of Fatality was impossible to win due to a glitch that [[UnwinnableByDesign did not recover the groove gauge at all, in addition to judgments other than Rainbow MAXes draining the gauge]] in the process. Thankfully, this was fixed ASAP.
* {{Bemani}} games in general usually have an unlockable Extra Stage with one or more "boss" songs, which are always among the hardest in the game. Do well enough on that and you'll get to play the TrueFinalBoss, usually named either "One More Extra Stage" or "Encore Extra Stage", and is generally the hardest song in the game (and [[SequelEscalation gets progressively harder with each subsequent installment]]).
** ''{{beatmania}} IIDX'' is known for having elaborate Extra Stage systems where, on your Extra Stage, you enter a special screen where you select one of several different boss songs. Completing all of these songs and fulfilling certain requirements on them (often a grade and special gauge requirement) will allow you to unlock and immediately play the system's FinalBoss.
*** ''beatmania IIDX 20 tricoro'' introduces the "LIMIT BURST" system, which uses crossovers from other Bemani games as bosses.
[[/folder]]

[[folder:Roguelike]]
* ''[[VideoGame/AncientDomainsOfMystery ADOM]]'' has quite a lot of these. Most of them reside in a BrutalBonusLevel and carry some artifact (indestructible powerful unique item) that drops when killed.
** There's Rehetep, an undead mummy lord, who "lives" in a pyramid filled with traps and maze-like corridors. The pyramid is impossible to enter until the player character hits level 13, when an invitation from Rehetep will magically appear. The reward for killing him is the Ancient Mummy Wrapping, which grants several very useful resistances and passive abilities.
** There's the Minotaur Emperor in the minotaur maze under a ruined city. He carries an axe that deals massive damage, but is also massively heavy.
** Then there's also the blue wyrm Srraxxarrakex, [[FragileSpeedster extremely fast quickling bard Filk]], the [[MightyGlacier complete opposite]] Emperor Moloch, and Keriax the multi-headed chaos dragon, who are all necessary to beat in order to reach the TrueFinalBoss.
* ''Videogame/DungeonsOfDredmor'': The real FinalBoss is Lord Dredmor himself, but a mistyped code in the third expansion brings you the chance of meeting Vlad Digula, prince of Diggle Hell. He's just about similar in magic prowess to Dredmor, has a bigger lifebar, but what truly makes him nastier is that trying to melee him without massive evasion rates is basically the quickest possible suicide you can find in a game with plenty of them.
[[/folder]]

[[folder:Role Playing Games]]
* ''VideoGame/ChronoTrigger DS'' had an Alternate Final Boss, the Dream Devourer, which has ties to the final boss of ''VideoGame/ChronoCross'', the Time Devourer. It is unlocked after you clear all three of the {{Bonus Dungeon}}s that appear after you defeat the normal FinalBoss.
** Before that, there's the [[BonusDungeon Dimensional Vortex]] fights against the Alabaster Shade, Crimson Shade, Steel Shade, and [[spoiler:Once-King Dalton.]]
** The [[BonusDungeon Lost Sanctum]] also has some, like the multiple fights with the Nu Guardian.
** The ultimate form of Spekkio is also one of the strongest bosses in the game. But since you need maxed out characters to even challenge him there is not much strategy involved anymore...
* The Gargoyle in Koudelka, on Disc 3/4. At the same time, it's also ThatOneBoss - because even for a bonus boss, it is just insane. Also, it's a HopelessBossFight on Disc 2 - when the titular heroine fights it alone, she'll deal no damage and will be forced to run away.
* The bounty bosses in ''VideoGame/SkiesOfArcadia Legends''. They are also ThatOneBoss - because even for a bonus boss, their difficulty is sadistic.
** However, the [[RandomlyDrops Rewards]] some of them leave make the rest of the game [[GameBreaker piss easy]]. Captain's Hat + Berzerker Mail anyone?
** The original game had a few as well. You don't have to fight any of the giant monsters (Obispo, the Roc, the Giant Looper, and Alania). There's also [[MetalSlime Elcian]], a super Looper who appears in the Dark Rift near the end of the game, who puts up a tough fight but gives good experience and loot and can be fought multiple times, making him great for LevelGrinding. And finally, OneHundredPercentCompletion unlocks one final battle against [[spoiler:Air Pirate Vigoro]].
* Ragu o Ragula in all of the ''VideoGame/WildArms'' games for PlayStation, PS2, and PSP. Angolmois also appears in some of them. In fact, the Wild [=ARMs=] games have many bonus bosses, often found [[SealedEvilinaCan sealed in crystals]] found throughout the game. Ragu o Ragula is neatly incorporated into all of these titles as the sleeping demon who is fated to destroy Filgaia, centuries after the conflict-of-the-day is finished off. Big extra credit for overachieving heroes. The other bonus bosses can range from CallBack characters, characters who are no longer a part of the main plot and have been more-or-less forgotten by the main cast, and [[ItMakesJustAsMuchSenseInContext nudie mags]]
* Gabriel Celesta and the Iseria/Isis/Ethereal Queen in ''ValkyrieProfile'', the ''StarOcean'' series, ''VideoGame/RadiataStories'', and ''InfiniteUndiscovery''... most tri-Ace games in general.
** Freya from ''ValkyrieProfile'' is the strongest boss in ''StarOceanTillTheEndOfTime'' where she makes a cameo appearance along with Lenneth.
* Ultimate Weapon and Khaer Magnus in {{Everlong}}. To mention just the really tough ones.
* They exist in pretty much every ''Franchise/FinalFantasy'' game:
** Ruby Weapon and Emerald Weapon in the international version of ''VideoGame/FinalFantasyVII''.
*** ''CrisisCore'' has Minerva. Genesis's best form is ''nothing'' compared to her.
** Ultima and Omega, or Ultima Weapon and Omega Weapon, appear in many of the games, including ''VideoGame/FinalFantasyV'', ''VideoGame/FinalFantasyVI'', ''VideoGame/FinalFantasyVIII'', ''VideoGame/FinalFantasyX'', ''VideoGame/FinalFantasyX2'', ''VideoGame/FinalFantasyXI'', ''VideoGame/FinalFantasyXII''. Omega also features prominently in ''DirgeOfCerberus''. Ultima was a mandatory boss in ''VideoGame/FinalFantasyVII'' as well as ''VideoGame/FinalFantasyVI'', under the name Atma Weapon. Omega and Ultima are storyline bosses in XI's Chains of Promathia expansion, and are {{Sequential Boss}}es to boot.
** The Monster Arena monsters in ''VideoGame/FinalFantasyX'', and the Dark Aeons and Penance in the International version. Some of the Dark Aeons were required encounters if you want to backtrack to certain areas. Penance is entirely optional, and he's accordingly brutal... 12 ''million'' HP, potent attacks that devastate an unprepared party, and supporting limbs that do even more fun damage.
** The Via Infinito monsters, led by Paragon and Trema, in ''VideoGame/FinalFantasyX2''. Black Elementals with the ability to just use Ultima at 255 magic whenever it wants, Chac for bypassing stone status resistances or debuffing all stats by TEN with Heaven's Cataract or Concherer who isn't too bad but IS a brick wall of defense.
** The Fiend Arena in the Internation/HD Rerelease has quite some nasty customers in their tournaments. Expect daunting foes Such as Bahamut with over 100,000 HP and a surehit kill attack for 9999 damage per girl (all used at leisure), enhanced human enemies (Baralai, Nooj, Gippal, etc) with jacked up stats and brand new cheapo moves to annihilate before a chance is had. The toughest though is Allmighty Shinra with potent spells meant to decimate the party right off the bat, and regular nasties such as Paragon and Trema above as regular battles.
** X-2 also gives us Major Numerus, a four headed, four staged boss with tons of abilities to decimate the characters. It's required to fight him with Three Iron Dukes equipped (one girl a piece) or else you're just wasting your time.
** Hell Wyrm, Yiazmat, Behemoth King, the eight non-story line Espers (which includes Zodiark), Omega Mk. XII, etc. in ''VideoGame/FinalFantasyXII''. To date, Yiazmat is the boss with the most HP in all of ''Franchise/FinalFantasy'' (a grand total of ''[[MarathonBoss 50 million]]''), and can take multiple rounds to defeat.
** ''VideoGame/FinalFantasyTacticsA2'' had Upsilons A1 (leveled somewhere in the 60s) and A2 (Level 96) and the Level 99 mage clan.
** ''VideoGame/FinalFantasyI'' had a [[BossInMookClothing special secret random encounter boss that was only able to be encountered on the walkway heading towards Tiamat.]] The boss was a mecha named Warmech and had damage capabilities surpassing Tiamat.
*** The remake in ''Dawn of Souls'' for the GBA included optional dungeons with bosses from ''III, IV, V'', and ''VI'', although only Omega and Shinryu from ''V'' were much harder than the regular FinalBoss.
*** The PSP remake ups the ante with Chronodia, who has 8 FORMS! It's not a SequentialBoss, though; which one you fight depends on how you did in the BonusDungeon prior to fighting her. Either way, she's pretty hard.
** ''VideoGame/FinalFantasyII'': On your way through the two {{Very Definitely Final Dungeon}}s, there are numerous {{Chest Monster}}s guarding VERY useful weapons and armor to have. They're not as strong as most Bonus Bosses, but then again, in [[NintendoHard a game like this]], '''everything''' is insanely strong if you don't go through literally half a week of stat grinding.
** ''VideoGame/FinalFantasyIV'' had four optional boss fights against [[SummonMagic Phantom Beasts]]: Ashura, Leviathan, Odin, and Bahamut. Only one of these was particularly difficult. The others required very specific strategies rather than a highly leveled party to defeat, making them closer to {{Puzzle Boss}}es than anything else. This was fitting, as the battles were intended to be [[DefeatMeansFriendship tests of your skill]]. Furthermore, several powerful weapons and armor in the final dungeon are guarded by horribly powerful PaletteSwap bosses, including one that hits the entire party with unblockable Doom when the fight starts (giving you a time limit before TotalPartyKill).
*** The GBA version added some more, most notably, a modified version of Easytype Zeromus.
*** The DS remake removed most of those added by the GBA version, but features two new optional bosses only accessible through NewGamePlus - Geryon and Proto-Babil.
** ''VideoGame/FinalFantasyVI Advance'' adds the bonus boss Kaiser Dragon, a monster that was DummiedOut of the original game and, due to having an associated monologue, seems to have been intended to have been a bonus boss in the original version, but to have been cut for time.
*** In addition to Kaiser Dragon, the entire BonusDungeon leading up to him is full of bonus bosses, in the form of souped-up versions of the Eight Dragons, each much stronger than other bosses in the game.
*** There are also three new boss espers - Leviathan, Gigantuar, and Gilgamesh.
*** ''Also'', there are five bosses found wandering in a pit within the Dragon's Den - Dark Behemoth, Abyss Worm, Gargantua, Earth Eater, and the Malboro Menaces. All but the Malboros are relatively easy to take down, though. On the other hand, you have the three bosses-in-chests: Neslug, Plague, and the Flan Princesses, which use massive recovery, Doom to all, and Berserk to all, respectively.
** ''VideoGame/FinalFantasyV'' had two of these, Omega and Shinryu, both who gave [[BraggingRightsReward trinkets praising your deed]] upon death, and who made Neo Exdeath look like a marshmallow peep in comparison .
*** ''Final Fantasy V Advance'' was especially brutal with these, creating an entire Main/BonusDungeon full of them. This included such prestigious opponents as [[spoiler:Enuo, the frickin' original creator of The Void, which was the Main/MacGuffin that was Exdeath's entire goal, and something that he couldn't control in the end;]] Omega MK II and Neo Shinryu, souped-up versions of the bonus bosses of the original game, both of whom made their originals look like marshmallow peeps in comparison (Omega MK. II was very notable, housing a huge floor full of copies of Omega, each one as strong as the bonus boss of the same name, proving just how much stronger the players had to be to stand a chance.)
*** Keep in mind that all of this being harder than the rest of the game is no mean feat - this was, after all, the ''Final Fantasy'' that was denied release outside of Japan first time around due to being too hard.
** Ozma (unique in that his difficulty has little to do with inflated stats and almost everything to do with proper strategizing, albeit with more than a hint of Main/GuideDangIt) and Hades in ''VideoGame/FinalFantasyIX''. Kinda complementary - Hades turns out to be a legendary synthesist, and one of the rewards for beating Ozma is something you can synth off to obtain Ark, the ridiculously over-the-top summon.
*** There's also the Tantarian, another boss whose difficulty is based on strategy rather than just stats. Beating him nets an accessory that teaches the very useful Auto-Haste ability.
** ''VideoGame/FinalFantasyXIII'' continues the tradition with two:
*** Vercingetorix, boss of the final [[SideQuest Mission]]. This bad boy has 15.8 million hitpoints and can't even be accessed until after you beat the game. But it's easier to beat by simply poisoning him and then guarding for the entire battle; this is because poison deals damage based on maximum HP, and Vercingetorix, as mentioned, has a ''lot'' of it. Long Guis, however, are immune to every form of status debuffs.
*** Long Guis also qualifies, having even more HP and huge stats.
* ''VideoGame/FinalFantasyXIII-2'' features several optional bosses, three of which are absolutely brutal. The Long Gui returns, and despite only having a quarter of the HP it had in XIII, it's still extremely tough to put down. Yomi is a weaker (but still formidable) version of Vercingetorix. And finally, there's Raspatil, a horrifyingly powerful Undying Cie'th that's probably the hardest fight in the vanilla game.
** The DLC Coliseum battles are all nasty, especially Jihl, the one person everyone who played XIII wanted to kill and now can't because of her summoning tricks and Sadistic Surge, and Gilgamesh, who has almost 10 million HP, can heal himself for 1 million after stagger, and once he reaches half HP, he goes into enhance power mode, complete with auto-haste and attacks that even a Sentinel can struggle to keep up with.
*** The most notorious monsters in the Coliseum, however, are Snow and Valfodr. First off, before you can fight Valfodr, you fight Snow, who has 10 million HP, and if you don't provoke him into attacking someone else and he continues to attack the same character for a set amount of time, he will use a TotalPartyKill attack that you cannot survive even if you use Sentinels.
*** Once you defeat him, you fight Valfodr. He has five forms, progressively getting harder. While Level 1 and Level 15 aren't too much to be concerned about, at Level 45, he summons monsters that constantly heal him and gains a powerful axe attack. At Level 70, he summons Chichu - the ever famous best commando in the game - and gains a group attack that can kill even a triple Sentinel party (Reprieve won't save you either). And while he doesn't summon anything at level 99, his attacks are even more powerful, and he's much quicker.
* ''Franchise/KingdomHearts'' loves these. They come in three flavors - "Disney character", "[[BossInMookClothing Insanely Powerful Mook]]", and "Walking SequelHook".
** [[VideoGame/KingdomHearts First game]]: The Clock Tower Phantom (gives you the last Stop spell upgrade), as well as many of the tournaments.
*** The international release [[RegionalBonus added]] [[VideoGame/FinalFantasyVII Sephiroth]] (bragging rights), [[Disney/{{Hercules}} Ice Titan]] (bragging rights), Kurt Zisa (bragging rights).
*** The Final Mix version adds in the international bosses, gives you decent rewards for beating them (extra Keyblades for Seph and Ice Titan, and the Zantetsuken attack for Kurt), and adds the Unknown, who is later revealed to be [[spoiler:Xemnas, the BigBad of ''VideoGame/KingdomHeartsII'']].
** ''VideoGame/KingdomHeartsII'': Sephiroth + tournament matches again. The Final Mix included multiple upgraded versions of the Organization (including the ones who had died in [[KingdomHeartsChainOfMemories the previous game]]), made [[spoiler:Roxas]] an actual fight instead of a CutSceneBoss, and filled the "Unknown" slot with a mystery Keyblade Master named the "Lingering Sentiment" who is later revealed to be [[spoiler:Terra's soul trapped inside his armor after Master Xehanort took over his body in ''VideoGame/KingdomHeartsBirthBySleep'']]. He is found via a portal at Disney Castle and is ''[[ThatOneBoss THE hardest boss in the entire game.]]''
** ''[[VideoGame/KingdomHearts358DaysOver2 358/2 Days]]'': Dustflier. He can be found before beating the game, in a late-game mission where the goal is to defeat six bosses scattered through Twilight Town in succession, and only appears after all six are dead. And while you can ''complete'' the mission by only taking out the first six, you have to go and finish Dustflier to fill up the extra portion of the Mission Gauge, which is part of HundredPercentCompletion. (Fortunately, ''358/2'' allows you to redo missions at will.)
** ''Kingdom Hearts Re:Coded'' has [[spoiler:Buggy Roxas]], a powered-up, Heartless version of the already [[ThatOneBoss very hard]] [[spoiler:Data Roxas]]. The best strategy to beat him is to nail down his pattern, spam Dodge Roll whenever he gets even near close to you and try to cheat his AI so that he doesn't uses ThatOneAttack [[TurnsRed when he's low on health, where all his stats are doubled and he becomes gigantic]]. [[ThatOneSidequest You need to beat him to earn the]] [[InfinityPlusOneSword Ultima Weapon]].
** ''Birth by Sleep'' brings its own BonusBoss, [[spoiler:Vanitas Remnant]], notable in that he only has one health bar because he's JUST THAT HARD TO HIT. If you heal yourself during the battle, he ''also'' heals himself. Completely. [[spoiler:Unless you use potions instead of magic.]] The Iron Imprisoners are a much less difficult example.
*** ''Birth By Sleep''[='=]s international release adds a new boss, the [[SarcasmMode imaginatively-named]] 'Mysterious Figure,' [[spoiler:revealed to be a time-traveling young Xehanort in Kingdom Hearts 3D]], a black-coated, dual-laser-blade-wielding mofo clearly in the same style as the first Final Mix's just as imaginatively-named Unknown. This boss has put the rest of the series's [[ThatOneBoss famously batshit hard bosses]] to shame. So far, the only known strategies for beating it are "Spam Dodge Roll with Ventus and pray" and "Spam Thunder Surge with anyone and pray".
*** The Final Mix adds three more that can be fought in the Mirage Arena: [[Disney/{{Pinocchio}} Monstro]] and the armors of Master Eraqus ("Armor of the Master") and Master Xehanort ("No Heart").
** ''Dream Drop Distance'' has [[RunawayBrain Julius]], featuring heavy defense and powerfully strong attacks. Not to mention one of his combos doesn't set off Once More, only Second Chance, meaning you WILL die if you're unlucky, and another attack so powerful that not only does it eat up basically all of your HP, but it disables your active command. God help you if you only pack one curaga and kept the cursor on it. The worst part, the only way to know which way to dodge for the attack is to use the bottom screen, which you never use during any other fight, to see where his icon is headed. And you're not allowed to bring your Dream Eaters into the fight.
* ''Franchise/{{Pokemon}}:
** ''VideoGame/PokemonRedandBlue'': Articuno in the Seafoam Islands. Zapdos in the Power Plant. Moltres on Victory Road. Mewtwo in Cerulean Cave after you become Champion. The use of cheats also enables the player to battle ''Professor Oak'' in the original ''Red/Blue'' versions, with a team of higher levels than the freaking Champion. Some fans speculate that he was a supposed to be a TrueFinalBoss and got removed from the storyline, but the producers forgot to remove his battle data, since BossRush Agatha of Elite Four states that he is a RetiredBadass. Sadly, he didn't get any battle data in ''[[VideoGameRemake FireRed/LeafGreen]]''.
** ''VideoGame/PokemonGoldSilverAndCrystal'': In the first Generation II games, the legendary that's not your version mascot also counts as a Bonus Boss; in ''Crystal'', both Ho-oh and Lugia also count, with Lugia being available only by talking to a man in Pewter City and Ho-oh only being available by catching the Legendary Beasts. Red in the [[VideoGame/PokemonGoldAndSilver second generation]] (though it's debatable whether he's this or the TrueFinalBoss, since the credits roll after you win). ''[[VideoGameRemake HeartGold]]'' [[TheRemake and]] ''[[VideoGameRemake SoulSilver]]'' have a boss Trainer that can only be fought by having a Celebi: [[spoiler:Giovanni]]. This Trainer isn't very difficult, however, and mainly serves to tie up some loose story ends. Those two games also have a bonus battle with Red, the player character from ''VideoGame/PokemonRedAndBlue''. He is the toughest trainer in the games to date, with all of his Pokemon over level 80. You have to massively level grind after the main game or transfer Pokemon from other games to stand a chance against him.
** ''VideoGame/PokemonRubySapphireAndEmerald'': Latios/Latias and Rayquaza in ''VideoGame/PokemonRubyAndSapphire''. In ''Emerald'', Rayquaza can be captured ''before'' you take on the Elite Four in ''Emerald'' (and Groudon and Kyogre take its place as {{Bonus Boss}}es). Steven turns from FinalBoss in ''Ruby/Sapphire'' to Bonus Boss in ''Emerald'', having stepped down from his position as Champion. You find him in a secluded cave in Meteor Falls with a team identical to the one he has in ''Ruby/Sapphire'', except ''twenty levels higher''. The 7 Frontier Brains at the Battle Frontier also count, as they are only available after you beat the Champion.
** VideoGame/PokemonDiamondPearlAndPlatinum: The Generation IV games, ''VideoGame/PokemonDiamondAndPearl''[=/=]''Platinum'', also give us Heatran, Giratina, Cresselia, and Regigigas; four legendaries that can only be encountered after you've beaten the main storyline and obtained the [[GottaCatchEmAll National Dex]] (with the exception of Giratina in ''Platinum'').
** ''VideoGame/PokemonBlackAndWhite'' have [[spoiler:Cynthia]] as their bonus boss, as well as [[spoiler:[[CreatorCameo one of the game's developers from Game Freak, Inc.]]]]. In addition, [[spoiler:Alder, the League Champion, previously TheUnfought due to story complications]], can also be challenged by challenging the Elite Four to a rematch. The Subway Bosses of Unova's Battle Subway, can be considered this after one defeats the Champion.
** ''VideoGame/PokemonMysteryDungeon'' games, and most Legendary Pokémon that have no relation to the plot in the second set of ''VideoGame/PokemonMysteryDungeon'' games.
** ''VideoGame/PokemonBlack2AndWhite2'' basically goes UpToEleven on this one, letting you battle [[spoiler:nearly '''all''' of the previous Gym Leaders from Generations I-V, from Brock to Drayden, in the Pokemon World Tournament or PWT. If you manage to conquer the regional tourneys and the World Leaders tournament, you get to fight all of the previous Champions (minus Iris) in the Champions League.]] Also, there is also [[spoiler:Colress, the Shadow Triad, the Striaton Trio (Cilan, Chili, Cress) in a Multi Battle, now RetiredBadass Alder, his grandson Benga, the [[CreatorCameo GameFREAK]] trainers, and under the right conditions, Cheren, Bianca, and '''N'''.]] There are plenty of powerful trainers to battle for the postgame.
** ''VideoGame/PokemonXAndY'' doesn't have as many of these bosses as the previous generation did. [[spoiler:For Legendary Pokemon, there's one of Kanto's Legendary Birds (Which one you'll face depends on the starter you picked), Zygarde, and the aforementioned Mewtwo. As for trainers, it is possible to challenge [[TheRival Calem/Serena]] to a rematch postgame, and going through Looker's postgame missions has you battle Essentia ''four times in a row.'']]
* Aec'Letec in the ExpansionPack of ''BaldursGate''. Although he's more of a FinalBoss to the expansion pack, said expansion pack is an optional sidetrack from the main story, he can be safely skipped after finishing Durlag's Tower and is much worse than the game's actual final boss.
** Kangaxx in ''VideoGame/BaldursGate 2'', who could only be hit by +4 weapons, and, in his demilich form, could cast the annoying insta-kill spell Imprisonment at will, which had the tendency to mess up romances if your love interest got hit. Kangaxx does have an AchillesHeel, however, in the form of a [[WeaksauceWeakness shockingly poor]] [[OneHitKill death save]] for his level.
** Most of the dragons in the game are also optional fights, though they give some good rewards after being slain.
** There's also an optional (and completely story-irrelevant) fight against some demon knights in the Underdark.
** In the expansion pack ''Throne of Bhaal'', the Bonus Boss was Demogorgon, an incredibly powerful demon imprisoned at [[Main/BonusDungeon the bottom of Watcher's Keep]].
** The Twisted Rune is an order of evil spellcasters who, when you enter their lair, assume that you've come to foil their plans and attack you. They're sensibly skeptical if you claim to have found them by accident, because the only way that would happen is if you were wandering around a bad part of town while carrying an incredibly rare and valuable type of gemstone and opening doors at random. (This is in likely exactly what happened, unless you looked at a guide. The clues that would lead you to them were never put into the game.)
* Divine Dragon/Divinegon in ''VideoGame/DragonQuestIII'' became available to fight after beating the game. You even needed to beat him five times to gain access to all of his wishes.
** The Game Boy Color version of this game introduced yet another bonus boss, [=GranDragn=]. Getting to this boss required you to complete such a long, boring, and ridiculous fetch quest that even the most hardcore and dedicated gamers have never seen him.
* ''VideoGame/DragonQuestVI'' has Nokturnus (better known as Dark Dream), who, thanks to his appearances in the ''Monsters'' series, is considered by many to be ''the'' quintessential BonusBoss of the series.
** Nokturnus actually gets a little more plot relevance than the average BonusBoss, in that during the story, you witness a king try to summon him to deal with the BigBad, only to be violently reminded that EvilIsNotAToy. Though, if you're strong enough to put Nokturnus in his place, he really ''will'' deal with the BigBad on your behalf.
* {{God}} in ''VideoGame/DragonQuestVII''. And the four spirits, which is the odd thing since they are supposed to be weaker storyline wise than both the Last Boss and God, yet you can't fight them unless you can beat God easily.
* The Dragon King in ''VideoGame/DragonQuestVIII''. Have fun with the Darksteel Dragon as well; he's basically a Metal Slime with a lot better attack, who attacks ''three times'', and, just for more fun, he has nearly 2000 HP.
* Half of the bosses in ''VideoGame/DragonQuestIX''. Of special note are the grotto bosses, [[spoiler:who are revealed to be fragments of the Grand Architect Zenus]], and the legacy bosses, the final bosses and some midbosses from every previous serial title (e.g. Dragonlord, Zoma, Estark, Rhapthorne, etc.) The best kind of PanderingToTheBase. You can even opt to give the legacy bosses the experience you gain from beating them, and they will level up each time, to a max of 99.
* In the ''VideoGame/{{SaGa}}'' series, most of the '''game''' is optional, including many of the bosses. ''VideoGame/{{SaGa Frontier}}'' does have a few optional bosses who are '''particularly''' difficult, including the Earth Dragon in the Bio Research Lab, and [[Main/TheComputerIsACheatingBastard cheating bastard]] Jotnar, who likes to employ his most powerful attack four consecutive times on his second turn.
* ''VideoGame/GoldenSun'' had Deadbeard, an undead pirate found at the bottom of Crossbone Isle, who guards the game's most powerful armor. One path to him contained another bonus boss, a weather controlling lizard. A third bonus boss had its own bonus ''Town'' outside the BonusDungeon, and was a gigantic acid frog.
** ''The Lost Age'' gave us the Star Magician, Sentinel, Valukar, and Dullahan. The [[FlunkyBoss Star Magician]] summons mooks to use Jupiter psynergy on you, buff and heal the Magician, and explode for huge damage. Sentinel constantly buffs his defense and is immune to all psynergy, meaning he gets tougher and tougher. Valukar can knock your Djinn into Standby and use your summons against you with Crucible. And [[MemeticBadass Dullahan]] can put every active party member's Djinn into recovery with Djinn Storm, gets three moves per turn, and hits like a runaway cement mixer.
** In ''Dark Dawn'', Star Magician and Dullahan get buffed up, with Star Magician getting three new mook types (Curse, Death, and Ghoul) and Dullahan getting Valukar's Crucible move. There's also the Ogre Titans, a group of five increasingly powerful physical attackers, and the Ancient Demon, who can take over one character with Demon Sign.
** In the early parts of ''Dark Dawn'', if you try to beat the Psynergy Training Grounds a second time, the Dim Dragon gets an upgrade, making it an early-game BonusBoss.
* ''VideoGame/SuperMarioRPG'' has three:
** Tiny martial arts master Jinx, who you must fight three times (after defeating his apprentice, Jagger). The boss lives in Monstro Town.
** ''Franchise/FinalFantasy'' ShoutOut Culex, a powerful magic-using entity from another dimension who attacks using four elemental crystals and is quite possibly harder than the game's FinalBoss. It too lives in Monstro Town.
** There's also Mokura, a green cloud monster that appears randomly in Belome Temple and has boss music playing during his fight, although he's not nearly as tough as the other two.
* ''VideoGame/PaperMario'':
** Bloopers who shows up every time you find a new shortcut in the sewer. Kent C. Koopa also blocks a road and makes you pay to pass; beating him lets you pass for free. Then there is a Dojo, where you can fight for bragging rights. The final blooper, Kent C., and the Dojo Master could all give Bowser a run for his money if he didn't have the Star Rod.
** There's also the [[BossInMooksClothing Anti Guy]], found guarding a chest in a dungeon halfway through the game and with HP and attack roughly on par with Bowser's penultimate form. He can be beaten straight-up, or you can exploit his SweetTooth to bribe your way to the chest's contents.
** In Chapter 8, if you intentionally flunk a quiz from one of the Bowser-faced stone doors, your punishment will be a NoHoldsBarredBeatdown against ''three'' Anti Guys. Easily the most difficult fight in the game, as Mario will initially be taking in the ballpark of 25-30 damage a turn with (unlike all the above bosses) no way to cheese your way out of it.
* ''VideoGame/PaperMarioTheThousandYearDoor'':
** Bonetail gives the game's final boss a run for its money (which is lampshaded by [[MetaGuy Goombella]]) and requires going through a dungeon with 90 consecutive battles (99 floors with a "breather" every 10) to reach him. He is a bit easier than the final boss, as you'll probably be better equipped and levelled by the time you reach him, and his attacks aren't as complex to deal with - he just has enormous attack power and endurance, and getting to him is a massive two hour-long ordeal.
** Atomic Boo, fought in Creepy Steeple if you enter the main hall and take the Spin Hammer attack to the swarms of Boos enough times. He isn't particularly hard, but knowing he even exists is a bit of a GuideDangIt.
* ''VideoGame/SuperPaperMario'' tripled it, though (unless you count Francis in chapter 8-2 as one). [[spoiler:The first of the three bonus bosses was really another version of the game's first boss. To even face the second boss, you have to clear a dungeon filled with even stronger enemies that are all pitch black, making distinguishing subtypes near impossible without Tippi/Tipptron until it's too late.'' '''Twice.''''' The third is the 100th Sammer Guy, End Boss, who, although weaker that the second Bonus Boss, is the only one that cannot be fought until after beating the final boss.]]
* ''VideoGame/MarioAndLuigiBowsersInsideStory'' has several: [[spoiler:The Shroob trio, the X bosses, and Bowser X.]]
* ''VideoGame/MarioAndLuigiDreamTeam'' also has [[spoiler:the X bosses, with giant bosses now having X forms. Taking Bowser X's place is Bowser Jr.]]
* ''Franchise/TalesSeries''
** ''VideoGame/TalesOfSymphonia'':
*** The game had at least 6 hidden bosses [[spoiler:(Seles, Abyssion, Maxwell, three former Tales characters (Woodrow/Garr, Farah, and Meredy), and the Sword Dancer, and the Living Armor at the end of [[BonusLevelOfHell Forbidden Anamnesis]])]], the second of which gives you [[InfinityPlusOneSword weapons]] that makes the rest of the game ridiculously easy - [[BraggingRightsReward as if it weren't already for anyone powerful enough to defeat him in the first place]].
*** During your first encounter with the Sword Dancer, you may or may not get fucked up almost immediately. His attacks are absurdly powerful in this encounter, being able to KO the '''ENTIRE PARTY''' with a ''single attack.'' Though, if Raine unlocked one of her spells, like the photon spell, then you can defeat it rather easily. The next two encounters are only moderately hard because you'll be appropriately-leveled and you'll be able to use Unison Attacks.
*** [[spoiler: Abyssion]] could give some {{Creator/Atlus}} bosses a run for their money. Because of the [[spoiler: [[ArtifactOfDoom Devil's Arms,]]]] he can [[MegaManning mimic every character's fighting style in rapid succession]], can cast the most dangerous spells in the game with barely any delay, hits like a freight train with both magic and physical attacks, and has '''[[DamageSpongeBoss 180,000 HP,]]''' ''three times'' as much as the FinalBoss. And he only [[TurnsRed gets]] [[UpToEleven harder]] when you reduce him to half HP. Martel help you if he goes into [[SuperMode Over Limit...]] [[SarcasmMode Even better,]] he is capable of using Genis's Indignation Judgement, and, in the PS2 version, he can also use Lloyd and Kratos/Zelos's final attacks as well. And finally, in the PS2 version? [[TheComputerIsACheatingBastard He's immune to All-Divides.]]
*** You fight Garr, Farah, and Meredy in the coliseum. They are absurdly hard to beat, in fact, think of having to fight Lloyd, Genis, Zelos, and Presea at the same time, while they use the very same battle strategy as you do, which is what makes them so hard. But once you get rid of Farah, then Meredy and Garr are almost a piece of cake, that is assuming you have enough healing items. The best party to fight them with are Lloyd, Zelos/Kratos, and Genis. Replacing Genis with Raine is also a good idea, but her lack of offensive spells may cause the fight to drag on. It's kinda funny hearing Lloyd say "Who the hell were those guys?" after beating them.
** ''VideoGame/TalesOfPhantasia'' had Pluto, who gave you his summon, and Odin, who is also a DuelBoss. Apparently, he really was ''that'' Odin.
** ''VideoGame/TalesOfEternia'' had Sekundes, the summon of Time, although you didn't have to beat him to enlist his services. Maxwell and Shadow were also technically optional, but you ''did'' have to beat them. Cless gives you his bandanna and the Eternal Sword if you beat him in the Arena, and Valkyrie stands before a ''lot'' of treasure chests. Things like this make ''Eternia'' end up a very long and interesting game.
** ''VideoGame/TalesOfVesperia'':
*** The "Traitor to the Heavens" ([[spoiler:[[VideoGame/TalesOfSymphonia Kratos]] fulfilling the role of a cameo boss]]). It also has a bit of an odd case with the Radiant Winged One, [[spoiler:who, while entirely optional, if the player opts to fight him, [[TrueFinalBoss ends up as the last boss anyway]].]]
*** There are also [[spoiler:[[VideoGame/TalesOfPhantasia Dhaos]], [[VideoGame/TalesOfEternia Shizel]], [[VideoGame/TalesOfDestiny Barbatos]] (who still HATES items), and [[VideoGame/TalesOfSymphonia Kratos]]]] as bosses in the 200 Man Melee.
*** The PS3 UpdatedRerelease adds several more optional bosses, such as Clint of the Hunting Blades, the Sword Dancers [[spoiler:which reward you with Flynn's normal, non-Fell Arm InfinityPlusOneSword]], and [[spoiler:the Spiral Draco, lord of the Entelexeia and possibly the most difficult boss in the entire Franchise/TalesSeries]].
*** There's also a colosseum fight where you use the four characters you currently have in your party against computer controlled versions of the other four you aren't using.
*** In addition to the already long list of bonus bosses in Vesperia, there's also Yeager's bodyguards, Gauche and Droite.
** ''VideoGame/TalesOfTheAbyss'' contains [[spoiler:Nebilim]], who's practically impossible to beat on your first playthrough, as well as Reid, Mint, Nanaly, and Philia.
** ''VideoGame/TalesOfGraces'':
*** The post-game boss Solomos, as well as all the other bosses in the [[BonusDungeon Zone Cage]] and Coliseum (including [[spoiler:Veigue, Kohak/Amber, and Reala as the previous Tales cameo battle]] and [[spoiler:Poisson]]. Defeating Solomos also ''changes'' the real final boss, [[spoiler:Lambda Angelus]] into [[spoiler:Lambda Theos]]. In addition, you can re-fight your first boss, although he is no longer the WarmUpBoss that he was before. You also can fight the incredibly large and strong [[AttackOfThe50FootWhatever Rockgagan]], although in the PS3 version, you only really get a [[BraggingRightsReward trophy]] for defeating him - not even experience points.
*** There's also the three dragons that correspond to the 3 Giant Cryas in each country. Good luck trying to take them on before beating the final boss cause even on Normal, it's not easy.
** ''VideoGame/TalesOfXillia'' has the Golden Swordsman at the end of its BonusDungeon. He's nothing to scoff at the first time you fight him, but he gets even stronger the next few times you fight him.
** ''VideoGame/TalesOfXillia2'' has a massive number of these compared to its prequel, all available after beating the game. Defeating all of the Giganto Monsters will result in all of them reappearing as their much stronger EX versions. The bonus dungeon is populated by shadow versions of numerous past bosses, your party members, and [[spoiler:[[VideoGame/TalesOfDestiny Stahn]]]] and [[spoiler: [[VideoGame/TalesOfPhantasia Cless]]]]. The end of EX Tag Arena pits you against powerful versions of past bosses partnered with random members of your party, plus if you defeat them quickly, you'll be rewarded with a bonus fight based on who your lead character is (Most notably, in Ludger's case, a stronger version of [[spoiler:''the final boss'']] shows up). Lastly, the end of EX Team Arena pits you against the cameo team of [[spoiler:Cless, Mint, Stahn, and Rutee]] in a battle that's chaotic enough to warrant a special ending scene should you prevail.
** Also, ''VideoGame/TalesOfHearts'' bonus boss is nearly IMPOSSIBLE without use of infinite aerial combos or cheats.
* The four-legged Dragons (not to be mistaken with the two-legged wyverns) in ''VideoGame/MonsterHunter'', as well as Kirin the lightning unicorn.
* ''VideoGame/DarkSouls'' has several in the optional areas of the game. The first one most players see is the Stray Demon, a much stronger version of the tutorial's Asylum Demon that drops a highly valuable Titanite Slab. Others include the magical Moonlight Butterfly in Darkroot Garden, the illusionist Dark Sun Gwyndolin in his father's tomb, and the half-Dragon Priscilla in [[BonusLevel the Painted World.]] The difficulty of these encounters depends on the player's progress through the game and they are much easier than the final boss, but they still provide a unique challenge to those who look for them.
** The DownloadableContent ''Artorias of the Abyss'' adds a new hidden BonusLevel with several bosses in it, all of them difficult fights. The bonus content even has its own bonus boss; while most of the bosses block off new bonfires and are normally accessible, the black dragon Kalameet is unlocked by a side quest and only gives the [[BraggingRightsReward Calamity Ring as a reward, which halves your character's health.]] Cutting off his tail creates a powerful weapon, but doing that is even harder than killing him. Adventurous players can also find a fight against two of the first [=DLC=] bonus boss at the same time.
* ''Videogame/DarkSoulsII'' has three:
** The Ancient Dragon is a brutal MarathonBoss with a lot of health and all of its attacks can kill you in one hit unless you have extremely high Fire resistance. The saving grace is that most of its attacks are fairly telegraphed and can thus be avoided rather easily. Except when it decides to fly up and rain fire on the arena. Avoiding that can be a struggle. Upon defeat, it drops an item that makes the next Bonus Boss easier.
** [[spoiler:King Vendrick]] is an AnticlimaxBoss whose attacks are slow and easy to dodge, though he can kill you in one hit if you aren't careful. However, he is also a PuzzleBoss since his defense is incredibly high, making him impossible to defeat if you don't have [[spoiler:Giant Souls]] in your inventory. Upon defeat he drops nothing. [[spoiler:The rewards appear behind a hidden locked door in a different area.]]
** The Darklurker is the most obscure. The previous two are at least encountered in the storyline. It is entirely possible to never encounter this boss [[GuideDangIt if you aren't playing with a guide]]. You need to discover and join an hidden covenant and fight through three small dungeons filled with dangerous black phantoms just to meet the Darklurker. Your efforts are "rewarded" with a harrowing battle against an eerie angelic figure who hurls powerful pyromancies, hexes, and sorceries at you while flying around the arena. It [[SquishyWizard thankfully has much lower health]] than the other two bonus bosses. Upon defeat, it drops its soul which can be traded for a powerful hex. Its defeat also maxes out devotion to the hidden covenant, which comes with its own rewards.
* In the ''VideoGame/MegaManBattleNetwork'' series, there is so much extra content and so many bonus bosses that the time taken to defeat them is longer than the main story line. In all of them, however, you face Bass/Forte. Unlike other continuities, here he is a god-like {{Badass}}.
** The sequel series, ''VideoGame/MegaManStarForce'' is similar, although it doesn't take nearly as long to do so. Usually there's a secret area after beating the FinalBoss where you have to fight upgraded forms of each boss in the game, followed by an all-new secret boss. After doing that, the storyline's final boss is upgraded, with it being the truly strongest boss in the game. The only exception to this is the second game, where after beating the upgraded final boss, you fight [[spoiler:an upgraded Rogue after the credits finish.]]
*** You can also engage a number of repeatable bonus bosses and random people who can Wave Change in ''2''. These include second shots at the storyline bosses to get their Mega cards, plus farmable bosses like Kung Foo Kyd, Gemini Spark, and Cancer Bubble.
*** In addition to the aforementioned styles, the third game has a rather unusual take on this with the Omega versions of the bosses, as they can rarely appear virtually anywhere in the game, and also at any point in the story, even before you've fought their regular versions. It's entirely possible to run into one of them ''right after the gameplay tutorial'', despite even weakest of them being far stronger then the final boss. Fortunately, the game is nice enough to not give you a game over for losing to them and also alerts you of their presence by changing the music in the area to a very ominous tune.
* ''VideoGame/MegaManXCommandMission,'' meanwhile, had two Bonus Bosses plus another set of nine. Rafflesian and Duckbill Mole gave X, Zero, and Axl new abilities that were useful in what remained of the game by that point. Ninetails and the preceding eight Tails Clan members, on the other hand, who were definitively even more this trope, could only be fought ''after'' beating the final boss, making the rewards for beating ''them'' [[BraggingRightsReward pretty much awesomely worthless.]]
* The 3 Golden Pigs at the end of the BonusDungeon (Mull's Dungeon) in ''AtelierIris'', which are significantly more difficult than the final boss.
* In ''VideoGame/{{Atelier Iris 2|The Azoth of Destiny}}'', the fights at the Dragon's Nest, particularly the last one against 3 Instant Brownies. However, while they are more powerful than the last boss, the overly-easy battle system makes them no more difficult than anything else, provided the player has stocked up on resurrection items.
* Kisuke in ''Manga/{{Bleach}}: Soul Carnival 2.'' The thing with him, though, is that he can be fought pretty early on in the game, not that you'd have any chance of survival then. Until you clear the Soul Society missions, he'll probably kill you with just one combo. Not to mention that he has two supports, whereas most bosses only have one, '''OR''' the fact that his Burning Attack can even hit you if you're off-screen, and it stuns you invariably (as Burning Attacks never miss). When you defeat him, you'll unlock him as a playable character.
* ''VideoGame/BreathOfFireIII'' had the Berserker, difficult because it attacked for three to four hundred damage, and often attacked several times before any of your characters got to. Worse, it was a [[BossInMookClothing random encounter]] on the way to getting one of your dragon genes, and was a normal monster.
** And in the same area was an even tougher BonusBoss, the Arch Mage. He has far less HP than Berserker (only about 3,000 compared to the Berserker's 15,000), but regenerates 1,500 of it every single round, which is more than most casual players can deal in a single round, and is capable of hitting just has hard as Berserker. In fact, if you have one living and two dead characters, Arch Mage will USE A SKILL THAT REVIVES THE TWO CHARACTERS. Presumably, he does this simply as a means of embarrassing you further.
* ''VideoGame/BreathOfFireIV'' has Rider as a hellish random encounter in Mukto. With 40,000 HP he is already a tough opponent but he also regenerates 20,000 HP every turn...try to overcome that.
* ''VideoGame/BreathOfFireDragonQuarter'' had Dover, who was the final boss in the BonusDungeon. As long as you have a high enough level (around 50), he's not that bad. The only problem is is that his defense switches from regular ol' attacks to Dragon defense. So your time limit is based on how much you have left on the D-Counter. [[SpellMyNameWithAnS Lin's/Rin's]] "Shatter!" technique is particularly effective here.
* The [[spoiler:Demi-Fiend]] battle in ''Franchise/ShinMegamiTensei'' game ''DigitalDevilSaga'', quite possibly one of the hardest bosses in the history of {{JRPG}}s, if not ''the'' hardest boss. Not only will he instantly kill you in the first turn if you have a "forbidden" move set (read: any passive or castable move intended to null, absorb or repel enemy attacks), but the strategy required to defeat him requires a very specific use of one usually worthless skill that you would ''never'' use in the main game (to wit, the Null Sleep skill, which nulls all damage one would receive while asleep). I have no clue how anyone could figure this out without the use of a strategy guide. Beating him unlocks an useful accessory that you can find midgame through the sequel.
** And even then, if you do manage to get him down to half health, his High Pixie will fully heal him. If you kill all of his demon companions, he'll insta-kill you. If you go in with any protective moves, he'll insta-kill you. Hell, even with the correct strategy, if you take too long to kill him, he'll just get bored and insta-kill you anyway. To add insult to injury, his battle music is the ''regular Nocturne battle music'', so he may be an uber hard bonus fight to you, but you're nothing more than ''a random encounter'' to him.
** [[spoiler:Satan]] in the sequel is likewise enormously difficult, if a lot less so than the [[spoiler:Demi-Fiend]]; you require to continuously cast Charge to boost all your stats to max so [[spoiler:Satan]] won't cast God's Breath, his insta-kill move. If you did so, good, he'll only cast Dekaja and put you back at square one. Hurt him enough and take too long and he will cast Diarahan, putting himself back at full health. Anyway, even without their instant kill skills, both are beastly difficult -- you ''need'' to cap out your major stats to even have a fighting chance, and ''then'' [[HarderThanHard there's the actual strategy involved]]... which simply fails half the time due to bad luck.
** Other Bonus Bosses in the duology include:
*** TheFourGods: Each appears in a different sector in the first game, each representing a specific element. Avoid repelling their elemental attacks or hitting them with their respective elements and they will go down fairly easily.
*** Huang Long: Appears high in the Karma Temple after killing TheFourGods. Hits like a truck with the Almighty-type Celestial Ray, which also slaps you with any ailment he wants. Has tons of HP and can cycle through several forms to make the task of damaging him harder. Still not as hard as the [[spoiler:Demi-Fiend]].
*** Beelzebub's two forms: Baal Zabul appears in Svadhisthana's underbelly once you unlock it with the Red Key. While he ''is'' somewhat strong, he's really nothing to be worried about. Beelzebub proper appears after Baal Zabul's defeat in the Manipura Waterways, and comes back with a vengeance, packing the lethal ''Death Flies'' move, which will kill anything not protected against Dark attacks with 100% effectiveness. Even if your charaters ''are'' protected, it will hit with a horribly strong Almighty-type attack.
*** Orochi is the last obstacle in the path to the Red Ring, required for another boss. He has ''eight'' actions on his turn, can exploit elemental affinities and Criticals with Ice and Lightning attacks, abuse Makakaja and Megidolaon, and has a crapload of resistances. However, he has pathetically small MP for a boss, and will try to restore his tanks with yours. With Null Mute, he turns into a joke after a few turns.
*** Metatron fights you after you enter Ajna with the Red Ring. He likes to abuse Makakaja, Revelation, and Fire of Sinai, which can hit several times for Almighty damage with the possibility of instant death.
*** King Frost appears at Coordinate 136 after the defeat of Mick the Slug. Finish the minigame of "find the key" and King Frost will appear at the Princess' Bedchamber. He spams Cocytus, which will almost always freeze, and summons overleveled Jack Frosts to pound you.
** In the second game, there are fights against the Four Archangels, Shiva, Vishnu, Jack Frost and Seth in the second. The Shiva and Vishnu fights also require you to find a special item for each, from Parvati for Shiva and Narasimha for Vishnu.
* {{Atlus}} loves making [[ThatOneBoss these noble fellas]] to rain Megidolaons upon us since the early 90's:
** ''VideoGame/ShinMegamiTenseiI'' and ''RaidouKuzunohaVsTheSoullessArmy'' has Beelzebub. ''Soulless'' is particularly vicious as he requires three items to be fought, all of which have to be acquired through ZergRush battles with 100 enemies each; these will tend to be DemonicSpiders. Then, he will be fought amidst ''another'' ZergRush. Pray none of your healing demons get Charmed, as he will use and abuse any attacks which can inflict said ailment to jack up his health.
** ''VideoGame/ShinMegamiTenseiStrangeJourney'' has the NGP-exclusive [[PowerLimiter Alilat]] and [[PhysicalGod Demiurge]], as well as Mother Harlot if your alignment is Law at some point after the DualBoss fight against Aniel and Kazfiel. (Note that you only have to be Law-aligned to unlock the door to her chamber; you can change your alignment afterwards, which allows you to face both Mother Harlot and Bishamonten, whose chamber has a similar lock to the Chaos alignment, in the same playthrough.) Alilat has the game-breaking combo of high Magic stat, Mind Charge, and Megidolaon-a nigh-guaranteed TotalPartyKill. Demiurge is a BarrierChangeBoss, has the even worse Big Bang, which deals even more raw damage than Megidolaon and Dekunda and Dekaja, regularly heals himself with Diarama, and has a ton of HP. Additionally, he's fast enough to dodge most of you attacks and has all of the deadliest elemental spells. Mother Harlot uses the Almighty skill Babylon Goblet, which is more powerful than Megidolaon and also has a high chance of causing Charm.
** ''RaidouKuzunohaVsKingAbaddon'' has Masakado and Lucifer.
** ''VideoGame/ShinMegamiTenseiI'' has Beelzebub as the ultimate Bonus Boss, but there were others, such as the series's first three Fiends: Daisoujou, David, and Pale Rider.
** ''VideoGame/ShinMegamiTenseiII'' brings back Beelzebub as the ultimate boss. There are also the Fiends, of which there are five this time: Alice, Hell Biker, Ghost Q, the Sage of Time, and Matador.
** ''VideoGame/ShinMegamiTenseiIIINocturne'' plays around with this. The bosses of the UpdatedRerelease are required for the new ending, but many consider them Bonus Bosses as well. These include all of the Fiends (save Matador and the first fight with [[Franchise/DevilMayCry Dante]]/[[VideoGame/RaidouKuzunohaVSTheSoullessArmy Raidou]] [[VideoGame/RaidouKuzunohaVsKingAbaddon Kuzunoha XIV]], who is required), Beelzebub, and Metatron.
** ''VideoGame/ShinMegamiTenseiIV'' has both the Fiends (Matador is one example) and the DLC Bosses ([[spoiler:The Four Archangels, Ancient of Days, Sanato, and Masakado.]])
*** The game also has a plethora of bosses that can only be fought in their respective challenge quests. While the majority of them pale in comparison to the monsters already listed (the main exceptions are Beelzebub ([[OnceAnEpisode of course]]) and the New Game + exclusive Astaroth), they still count since most challenge quests are optional. Other than the aforementioned opponents, there's one particularly strong Bonus Boss for each route (though they don't compare to the Fiends, DLC Bosses, Beelzebub, and Astaroth, they're still stronger than other Challenge Quest bosses): [[spoiler:Mastema for Law, Demiurge for Chaos, and Shiva for Neutral, with the first two coming form Challenge Quests and the last being the Terminal Guardian's final battle]].
*** Special mention must go to the Fiends. Seven of these Fiends (Matador from above being one of them) can only be found in certain locations and the chance of actually encountering them is very low (1 out of 256). Each one has at least five Press Turn icons, will always get the first strike, and will spam Antichthon (massive Almighty damage and all stats lowered) if they cannot safely attack you or your demons with their preferred attacks. Defeating them will unlock them for special fusion, and often, a wonderful reward, including some of the game's best equipment.
* The ''VideoGame/{{Persona}}'' series:
** {{Persona 2}} was the Persona series' first entry in this list with Philemon's brutal bonus battle on his EX Dungeon.
** ''VideoGame/{{Persona 3}}'' has Elizabeth, although she can only be fought on the second playthrough by accepting her 55th request and going to the top of Monad. Although she seems to be nothing more than a thin blonde girl dressed like a bellhop, she is the most powerful foe in the game, can only be fought one-on-one (she'll kill any other party members right away), gets to attack twice every turn (where you can only attack once), has multiple personas and powerful attacks, and heals herself completely when at low health. Even worse, if any of her attacks are nullified, reflected, or absorbed (which they invariably will be, considering her attack rate and huge range of attacks), she goes berserk and spams a 9999-damage attack (out of max possible HP of 999) nonstop until you die. Amusingly enough, the UpdatedRerelease version of the game features an upgraded version of your starter Persona which seems to be tailor-made to fight her, as it resists every type of attack, giving you a good overall defense against anything she tosses out and avoiding driving her berserk.
** While nowhere near as insane as Elizabeth, the Reaper that can be fought in both version of P3 is no slouch when it comes to making a normal player tear their hair out. It's fond of casting spells that hit the whole party for 700-800 damage and going insane on unblockable "almighty" spells if the player sets up reflecting items. This one is more infuriating to the average player due to the fact that he appears when the player spends too long in Tartarus, the game's central randomly generated dungeon.
** ''Persona 3 Portable'' allows you to fight Elizabeth's brother Theodore if you make the proper choice early on in the game (it's not dependent on gender, apparently). However, it cranks things up to 11 with the Vision Quest, which not only contains more difficult versions of the Arcana Shadows, but also allows you to fight [[spoiler:Margaret! Yes, the one in the next example. You can still use your full party, but that doesn't make things any easier...]]
** ''VideoGame/{{Persona 4}}'' continues the tradition with Margaret. While you can bring in party members and she won't (immediately) wipe them, she's just as frustrating. Nice changes include only healing once. She'll still 9999 Megidolaon you if you bring in a forbidden item, and dump lesser ones on you every 50 turns. She'll also exploit 1 More relentlessly if you give her the chance in the pattern.
** After defeating a dungeon's main boss, a new, optional boss appears in the original's place. These tend to be [[EarlyBirdBoss a few orders of magnitude harder]].
* ''VideoGame/DevilSurvivor'' brings in the Fallen Morning Star, Lucifer, for its battle. While insanely difficult (infinite range, level 99, etc.), beating him does give you the ability to fuse him. Most people just take advantage of the fact that Recarm gives the revived the next turn to attack, and just suicide run him.
** Though your strategies are moot if he manages to get Megidoladyne off a couple of times, since every cast boosts its power until the 4th/5th is LETHAL. The first already does 500-600 on everyone!
** There are a bunch of other, lesser bonus bosses as well.
*** Ghost Q shows up on Day 3, offering treasure. If you select the correct card (it's totally random), you can complete his stage without having to defeat him, but the other cards turn into doubles of him.
*** Ikusa shows up with a swarm of powerful undead on Day 5. He revives the ones you defeat, and furthermore, you have to prevent any of them from reaching a pair of escape points while you battle him, then clean up after he's gone.
*** Also in Day 5, Nebiros. He appears surrounded by a lot of Vile demons with healing capabilities, meaning he can hide behind them and hit you from afar.
*** Sage of Time shows up on Day 6, hypnotizing civilians. If any of them make it all the way to him, he'll take their souls and you get a game over. You can wake them up to get them to start heading away from him, but if a demon gets them before they get away, same result. Later on the fight, the Sage will brainwash more civilians into entering.
* ''VideoGame/DevilSurvivor2'' has a whole slew of these (Ghost Q, Sage of Time, Billiken, Belial, Nebiros, Lilith, Beelzebub), culminating in Alice, each with a different gimmick:
** Ghost Q shows up at a time when you only have the MC in the party--you actually can get one other character into your party before engaging him, but he won't fight you. Also, if you defeat all of the other demons on the field before finishing him off, he'll run away.
** The Sage of Time will fight you with mid-tier demons when you're far too underleveled to be able to equip any of the heavier-hitting moves in your arsenal.
** Belial will hit the entire map with Gomorrah Fire, so you and your demons need to, at least, Null Fire.
** Nebiros will appear in a gaggle of undead and continuously summon more if you kill them, and BodySurf into them if you instead choose to go after him.
** Lilith sics a bunch of hypnotized civilians which you have to avoid killing with immensely strong demons, ''and'' her Temptation skill will wreak havoc amongst enemy leaders. Worse, any male leaders hit by Temptation will be charmed without fail, even with Null Mystic. Female leaders aren't charmed just as unfailingly, but there ''is'' a chance Lilith can charm them anyway.
** Billiken is a fairly standard battle, except his battle is the first one in which you can crack Holy Dance, and unless you abuse the hell out of the movement skills, he's programmed to go straight for the Pazuzu that has it and one-shot it. He can also steal money from enemies; if he manages to deplete your wallet, he can hit you with Barrage Strike, which hits for a lot of Almighty damage.
** Beelzebub is a vicious BarrierChangeBoss with a nigh-flawless defense and incredible attack, with a continuous stream of overleveled {{mook}}s.
** Finally, Alice isn't as difficult as Lucifer, but she does have Belial and Nebiros fighting with her, both with their signature tricks. Alice herself can easily oneshot entire parties with ''Die For Me!'', remotely drain them to death with Vitality Drain, revive Belial and Nebiros, and speed up their turns. Belial doubles as a callback to the first ''VideoGame/DevilSurvivor''.
* ''VideoGame/NeverwinterNights2'':
** Tholapsyx the red dragon. Quite possibly the hardest boss in the game, thanks to her size and fire attack; buffing the entire party (preferably with Energy Immunity: Fire and Stoneskin) and micromanaging spellbooks is almost mandatory, as opposed to the final bosses, whom you can just whack with sheer force if the party is well-equipped. The reward is 200,000 gold for your keep plus an insane amount of loot, including a cool weapon for paladins and clerics who bothered to take a certain quest in the keep.
** ''[[ExpansionPack Mask of the Betrayer]]'' has its own bonus boss, a seemingly harmless badger spirit that turns into a Gigantic Angry Badger of One-hit-kill Doom if you manage to anger it. Killing it nets one one of the only items in the game to grant permanent haste status (barring the time-consuming item crafting).
** Also in ''Mask of the Betrayer'', if [[MindHive One of Many]] is in your party when you meet the dead god Myrkul, they'll ask if they can eat the god's remains. Unfortunately, rather than eating souls outright like the PlayerCharacter's curse, One of Many adds consumed souls to its collective. Thus HilarityEnsues when [[AssimilationBackfire Myrkul overpowers One of Many and takes over]].
** In ''Storm of Zehir'', you can encounter One of Many on the world map, who will probably be impossible to beat the fist time you encounter it (you're thankfully not forced into a fight with it). However, due to the WideOpenSandbox nature of the game later on, you can return and fight it once you're sufficiently leveled. Beating it will earn you the Imarskarcana, a helmet with good spell resistance, the ability to summon a demon once per day and a few other perks. If you don't want to fight it, you also have the option to feed it your companions for experience points.
* The ''VideoGame/EtrianOdyssey'' series as a whole has a '''''LOT''''' of bonus bosses; many of them are usually part of {{Side Quest}}s.
** To start off, by the middle of the game, you can meet the first Bonus Boss, Wyvern, who is probably about 30-40 levels harder than your current, probably level 20s characters. Then you'll eventually meet three more bonus bosses, Golem, Alraune and Manticore; the former is a seriously extreme MightyGlacier, the second loves to spam StandardStatusEffects, and the last one combines both.
** Most excruciating are the four post-game bonus bosses: The three dragons and [[TrueFinalBoss Primevil]]. Each dragon has a breath weapon that can instantly wipe out your party on turn one. You can't beat them without having a protector with antivolt/antifire/anticold lvl.5, and Primevil has all three of those instant death attacks, so your protector has to have all three anti skills, and you need a turn guide so you know when to use which antimove. And you can still outright die if he uses his "disable all skills of all characters" move. You had to pray he didn't use it, or kill him very quickly. Good times, good times.
** Its sequel, ''Heroes of Lagaard'', also has a slew of bonus bosses. The dragons return, as well as a new TrueFinalBoss and even more SideQuest bosses, some of them already accessible before you beat the game.
** The next sequel, ''The Drowned City'', ''doubled'' the number of bonus bosses from the previous games, both new and recurring, and this time, there are far more {{Bonus Boss}}es you can unlock via {{Side Quest}}s ''before'' you beat the game even once. Cue the much-needed level grinding for the BonusDungeon.
* Panthera Cantus from ''VideoGame/TheWorldEndsWithYou'' is the toughest boss in the entire game. It has the highest attack power of all the Noise and two separate bodies; [[spoiler:a tiger on top and a lion on the bottom]]. The fight itself can be quite hectic and requires the player to pay absolute attention to what is going on in both screens.
** In addition, there are four "Boss Noise" on various days (Progfox, Grindcore Minks, Wooly AOR, and Goth Metal Drake), blue Noise symbols that lead to fights against ''much'' stronger Noise than average. For HundredPercentCompletion, you have to beat them all on Hard. Feel free to whimper.
** And in addition to THAT, additional Boss Noise symbols for every non-Bonus Boss except for the FinalBoss appear on various days after beating the game. This is more of a convenience for those going for HundredPercentCompletion, since you don't have to go through the entire chapter to fight the boss again, and can retry the fight if you didn't get what you were looking for, with the exception of the FinalBoss, which is annoying since that day has three bosses beforehand. [[spoiler:And, yes, as you may have feared by reading below, Reaper Beat and Taboo Minimimoto show up as Blue Noise as well. And, yes, you have to beat them on at least Hard in order to get all of the Secret Reports. [[RuleOfThree And, yes,]] you still need to beat Minamimoto, the harder one, on Ultimate to complete the Infinity + One Pin Deck.]]
** Unfortunately, some of these bosses were timed fights, so on your first time through, [[HoldTheLine you won if you managed to survive for 30 seconds]]. No such escape clause in the post-game, and many of these bosses are still intimidating, even having killed the final boss.
* The Black Rabite from ''SeikenDensetsu3''. [[KillerRabbit Evil in its cutest form!]]
* ''VideoGame/IcewindDale II'' has two of these, both within the same chapter. The first is a [[spoiler:black dragon in the "Crossroads", which can be killed to close the teleport to Kuldahar.]] Players don't actually have to fight it, and can achieve their goal in a much easier way, but the difficulty of the battle alone makes it worth it for many players. The other boss is [[spoiler:the Six Lost Followers, in the Kuldahar graveyard. This is regarded by many to be the hardest fight in the game, because A) there are six different enemies to fight at once, B) they are several levels higher than your party, and C) because each has only a few specific weaknesses, being immune to all other forms of attack, and with the weaknesses being different between each member.]] Victory gives the player the Holy Avenger, the best weapon in the game. Unfortunately, this pisses off quite a few people itself, as the weapon can only be wielded by a Paladin, meaning that there is no reward for anyone without a Paladin in their party.
* The Gundam RPG ''VideoGame/MSSagaANewDawn'' has Ultima Gundam and Omega Gundam, made from a mix of parts from ''Anime/MobileFighterGGundam'' and ''Anime/MobileSuitGundamWing'' mecha respectively. Their names are obvious [[{{Homage}} homages]] to ''Franchise/FinalFantasy'''s perennial BonusBoss pair, Ultima Weapon and Omega Weapon.
* ''LiveALive'' features several bonus bosses. The caveman chapter has King Mammoth, who offers a decent reward in the King's Fang, as well as the randomly dropped "Soda." The ninja chapter has two, one which offers a weapon that you can also get at the end of the chapter if you don't kill anyone, and another that drops an item that can deal a decent amount of damage if used in battle. The final chapter has about five, four of which drop the most useful equipment in the game.
* ''VideoGame/ParasiteEve'' had a few in the [[BonusDungeon Chrysler Building]]. While most of the bosses are color swaps of the storyline bosses, the giant cockroach and giant bee were exclusive to the building. [[spoiler:The original Eve is at the very top of the building, and defeating her gets you a different ending.]]
* ''LostOdyssey'' has seven: Persona, King Kelolon, the Cave Worm, the Blue Dragon, the Holy Beast, Legendary Spirit Sorcerer Fu, and The Immortal One in the Backyard.
** Players with access to XBox Live can get a new downloadable dungeon with an extra boss [[spoiler:Professor K, aka The Killalon]].
* ''VideoGame/GrandiaXtreme'', rather than a new and unique boss, gave you the chance to go back to the old dungeons after beating the final boss, and in one of them you can fight a super-powered level 200 version of a boss you already faced.
* ''VideoGame/MonsterRancher Advance 2'' features Ragnarok, a wandering special Dragon who only appears after beating the final boss. He will only appear to fight you once a year, and only if you have a specific kind of monster on your farm. If you're not prepared to fight him on the week he comes to visit, too bad for you! His stats are extremely high (especially considering when your monster can first fight him), and he's tough.
* ''VideoGame/TheLegendOfDragoon'':
** In the dungeon before the PointOfNoReturn, you are given the opportunity to fight the spirits of the three dragons you defeated. They drop some useful attack items, and they're also guarding chests containing powerful equipment.
** There's also the Poltergeist-posessed armor set in Fort Magrad, an optional section of the Snowfield on Disc 3 (you travel through this area on your way to Velwebb. Hint: the sword has an instant-kill attack and it always uses it at the character who manages to dispatch it.
** There's also the four Dragoon ghosts in Velwebb, and not to mention Magician Faust at Flanvel Tower, who is the most powerful enemy in the game. Beating him does get you a great reward though in the Phantom Shield along with 30,000 gold. Here's everything you have to go through to get to him, which definitely puts him in this trope by the above definition: Throughout the game, there is a side quest to collect a total of fifty stardust scattered throughout the continent. Every tenth stardust, when shown to the proper character, will give you a different item. The final item is a mirror that is required in order to face Faust. Faust is an insanely powerful Wingly who was second-in-command to Melbhu Frahma, but ends up being a dozen times more dangerous, possibly due to having been alive and studying/training for the entire time his "boss" has been asleep. You then have to find the entrance to Flanvel Tower, following a winding maze of teleporters just to get to the tower. If you do not have the mirror in your possession the first time you see him, he WILL kill everyone in your party with one blow a piece, and you will be unable to touch him. As it turns out, this first Faust is merely a projected image. The real Faust is able to cast his magic through the image even while being twice as deep in the dungeon. And so, obviously, you must finish the maze.
* ''VideoGame/RivieraThePromisedLand'' has Hades, the boss who only appear in the extra content section after you complete the game and obtained the Key to Hell from the Zombie Dragon in chapter 6. His Breakout does heavy damage, but he only attack once every 3 of your each character's turns (estimated), so if you keep healing yourself with elixer and attack him, he's a pushover. Of course, the final boss can has its HP brought down by 53% with [[InfinityPlusOneSword Fanelia]]...
* All the ''VideoGame/{{Geneforge}}'' games have an 'Expert' level dungeon with the toughest BonusBoss in the game. Most of them generate repeated creations to add to their attack power, and traps that deal extra damage unless the player has the skill to disable them or at the least reduce their effect. The worst is the Titan of ''Geneforge 4'', which each time it was weakened to low health would shift to a new form, with a new set of attacks, defenses and vulnerabilities, requiring the player to have mastered a wide range of combat abilities. And of course, leaving the dungeon to rest also reset this Boss to its original form and strength.
* ''VideoGame/BahamutLagoon'' has special "side quests" - essentially single battles - available throughout the game. One of them, appropriately named Hard Dungeon, is only available in the last seven chapters and is far more difficult than the final boss.
* All three episodes of ''VideoGame/{{Xenosaga}}'' have some:
** Episode 1 has four: two mechas, Din Gareth and Jin Gareth, the sharpshooter Great Joe, and Mintia, an evil version of MOMO.
** Episode 2 has a metric-buttload of optional bosses encountered in the game's many sidequests.
** Episode 3 has two mechas: Omega Universitas [[spoiler:AKA [[VideoGame/{{Xenogears}} Id Weltall]]]] and Erde Kaiser Sigma. The latter is the only mecha in the game who's fought without the use of E.S.s.
* ''ManaKhemiaAlchemistsOfAlrevis'' had 5 Bonus Bosses in total: four that were cameos from other Gust games, and the fifth is a PaletteSwap of the TrueFinalBoss. Each of them are fought individually, but later three of them can team up for a sixth battle, which can be ''very'' difficult if the player's not prepared. The only saving grace for that battle is their common [[WeaksauceWeakness vulnerability to a certain character's]] ''[[WeaksauceWeakness normal physical attack]]''.
* After beating Machinedramon and finishing the main story in ''DigimonWorld'', you can continue the story and find a new level with high powered {{Mook}} Digimon. At the end is Machinedramon once again, only this time his health is maxed out at 9999 and his stats are also quite high. This is all for bragging rights.
* While it's "only" a Mod, the ''KnightsOfTheOldRepublic Brotherhood of Shadow'' [[spoiler:has a flashback to Malachor V]]. You're pretty much stripped of all your gear, and [[spoiler:have to re-create the single-combat against Mandalore that ended the Mandalorian Wars]]. Comparatively, the canonical FinalBoss fight against Malak is nothing.
* ''VideoGame/{{Mother 3}}'' features several. First there is Lord Passion, who carries Duster's [[InfinityPlusOneSword Infinity Plus One Shoes]], Lil Miss Marshmallow guards a decent weapon for that point of the game, and the King Statue is just there for experience and is ridiculously easy if you know what to do.
* The Doppelganger in the ''[[DotHackGUGames .hack//G.U.]]'' games is optional, but is ridiculously difficult and gives some of the most powerful weapons in the games.
* The Xbox 360 game ''BlueDragon'' has several Dragons that don't ''need'' to be beaten, but give the player a useful accessory if they are. Genuine Bonus Bosses include the Gold Mecha Robo, the King Poo, and the Golden Poo.
* ''VideoGame/DragonAgeOrigins'' has several optional bosses among its many sidequests. The Revenants are powerful undead warriors that are managable on their own but get downright nasty with backup such as the ones that drop the Juggernaut equipment. Gaxkang the Unbound is an homage to Kangaxx from ''VideoGame/BaldursGate''. [[spoiler:Flemeth]] shapeshifts into a High Dragon. An actual High Dragon (who ''could'' be beaten easily if you surrounded it with [[UselessUsefulSkill Traps]] before you aggro). And many more.
** The expansion gives us the Queen of Blackmarsh, a [[NinjaPirateZombieRobot lightning-breathing spectral dragon]] who is quite unambiguously even more powerful than the FinalBoss. Also, the ''[[BrutalBonusLevel Golems of Amgarrak]]'' {{DLC}} has the Harvester, widely regarded as the toughest boss in the entire ''Origins'' saga.
** ''VideoGame/DragonAgeII'' helpfully marks its bonus bosses with dedicated Achievements you get for offing them: a Varterral, a High Dragon, Xebenkeck the Desire Demon (who happens to be an old chum of Gaxkang from part one), and Hybris the Pride Demon. The last one is [[ThatOneBoss particularly bad news]].
* ''[[Franchise/{{Naruto}} Naruto: Path Of The Ninja 2]]'' has the Kumite Dojo, which has many bonus bosses.
* ''VideoGame/ResonanceOfFate'' pits you up against [[spoiler:Sullivan and Rebecca]] at the end of [[BonusDungeon Neverland]]. Unlike many examples on this page, they are generally considered pushovers, especially compared to what you fought to get to them.
* ''VideoGame/TheSpiritEngine2'' has a variant: the bonus boss, Urtat Underval, is fought roughly halfway through the game rather than at the end. Another variant is that you fight him twice; [[spoiler:once as a human, and once as a hulking zombie]].
* ''VideoGame/{{Dubloon}}'' features [[MusicalAssassin The Quartet of the Seas]], a group of four bosses each found in one corner of the ocean. Alone, they aren't dangerous, but just wait until you fight them all four at once in [[BigBoosHaunt the Pirate's Graveyard]]. They ''will'' kick your ass.
* ''VideoGame/SandsOfDestruction'' has plenty, including a few solo bosses involving Toppy, Kirie, and Agan.
* ''VideoGame/{{Ys}} VI: The Ark of Napishtim'' has Majunun, a blowfish-like creature that guards the Eldian Orb and will kill you in one hit the first time you can access it. Just finding it is a GuideDangIt, and to have a chance of winning at all, you need to nearly max out your EXP, which takes many hours, as all the enemies only give 1 EXP on the highest few levels.
* ''FossilFighters'' has a ''huge'' slew of bonus bosses, one of which opens up before the final boss, and the rest of which appear afterwards, in the PlayableEpilogue.
** The lone bonus boss available before the game's end is Petey, a dino battler who demands to fight a team of three specific dinosaurs. If you take the time to grind those three specific dinos, he's managable, but if you're anything less than maxed, be prepared to hurt from it.
** But ''after'' the final boss? Both Saurhead and the [[TerribleTrio BB Trio]] reappear with "marathon battle" bosses, where you have to beat three of their teams with no break in-between. They're tough, and your reward is [[spoiler: the OlympusMons]] from waaay back at the game's halfway point. You can finally fight Dr. Diggins, though he offers up nothing but [[BraggingRightsReward bragging rights]] (and EXP, if you're looking to grind). You can fight a samurai who's been in the hotel room next to yours [[ChekhovsGunman for the entire game]], whose most notable trait is that his Trainer rank is [[UpToEleven one beyond "Master."]] Oh, and if you're feeling lucky, punk, you can go back to [[spoiler: the dinaurian spaceship]] and challenge [[spoiler: Duna, Raptin, and Dynal--all at once.]] And ''that isn't even all of them!''
** The sequel, ''Fossil Fighters Champions,'' follows suit. In addition to almost all of the important characters having high-ranked teams you can fight in the PlayableEpilogue, there's an entire ''bonus tournament'' that culminates in a fight against [[spoiler: Rosie from the previous game.]] There were also DLC bonus bosses--including a strange character named Ryne, who gives you a new legendary vivosaur for winning, and [[spoiler: Duna, Raptin, and Dynal again]].
* VideoGame/{{Fallout}} has had several of these across all the games in the series.
** VideoGame/{{Fallout 3}} Has five or six [[AttackOfThe50FootWhatever super mutant behemoths]] who you can hunt down. Admittedly, one is a MiniBoss over the course of the main story, but even then, you could just skip the entire section. Other optional bosses include Commander Jabsco of Talon Company, Lag-Bolt and Enclave Squad Sigma in ''Broken Steel'', and the three Ant Queens.
** VideoGame/FalloutNewVegas has the BigBad himself, Caesar. Especially compared to his second in command, Legate Lanius, Caesar is pretty weak for a boss, only being about as tough as an EliteMook. However, he's in the middle of the Legion's stronghold, and his personal section (the only one you're allowed to visit) is crawling with dozens of Legion troops. When you get past them, he is protected by eight {{Praetorian Guard}}s armed with [[PowerFist shotgun fists]], each of which is as powerful as him. At lower levels, Caesar and his guards will usually dogpile you into a corner and beat you to death in a few hits, since said shotgun fists do ridiculous damage and Caesar and his guards are ''fast''. However, if you go there at a later level with a good companion and high level weapons they'll go down easily enough.
** The four (five with Old World Blues) legendary creatures in New Vegas, which are [[UndergroundMonkey reskinned]], upsized, and [[ThatOneBoss overpowered]] versions of their normal species. Admittedly, a sufficiently leveled character can make short work of most ([[spoiler: Legendary Cazadore, Legendary Nightstalker, and Legendary Fire Gecko]]) but the [[spoiler: Legendary Deathclaw]] from the main game, and [[spoiler: [[LethalJokeCharacter Legendary]] ''[[TheGoomba Bloatfly]]'']] from ''Old World Blues'' can usually kill you in... Two hits. Almost always.
** There's another boss Deathclaw in Lonesome Road, named Rawr. It's a LightningBruiser, even compared to the Alpha Male, and will kill most characters in one hit, although it has somehwhat less HP than the Legendary Deathclaw. Defeating him allows you to build one of the most powerful Unarmed weapons from his talons, Fist of Rawr. [[spoiler: Or [[Manga/FistOfTheNorthStar Fist of the North Rawr]] if you have [[SillinessSwitch Wild Wasteland!]]]] There's also Gaius Magnus and Colonel Royez, who are only available [[spoiler:if you choose to nuke the Legion or NCR respectively at the end.]] The latter has all of his SPECIAL stats maxed out, the third highest HP of any human enemy after Ulysses and Legate Lanius, a Damage Threshold of 24, wields a plasma caster with overcharge ammo, and regenerates his HP very quickly from the radiation.
* ''VideoGame/BatenKaitos Origins'' gives us a few. There's [[spoiler:Nasca, Valara, Heughes, and Wiseman]], who are fought to tie up loose ends; one of them allows access to the game's TrueFinalBoss. There's also Arma Prototype M, a.k.a. The Wicked Gawd, who is the final boss of the Coliseum and is ''absurdly'' hard.
* In ''AlphaProtocol'', the BloodKnight ActionGirl SIE will offer to team up with you during the mission where you first encounter her. You can agree to the alliance, or you can attack her (or you can agree, complete the mission, then attack her when you encounter her again at the end of the mission). Not only will she not die when you win, but [[RelationshipValues your rep with her will increase]].
* ''VideoGame/{{Xenoblade}}'' has 5 bonus bosses wandering around the world that are above the player's maximum possible level of 99: Final Marcus at 100, Ancient Daedala at 105, Despotic Arsene at 108, Blizzard Belgazas at 114, and Avalanche Abaasy at 120.
** One long sidequest chain [[SidequestSidestory with its own story]] that covers almost half of the game leads to a bonus boss. Though this one is not overleved, it stands out because [[spoiler:the boss is one of the [=NPC=]s the team has been doing quests for, Bana the Nopon, the battle is under a tune only reserved for a few select {{Hopeless Boss Fight}}s]], and the quests that lead to it can be LostForever.
* ''VideoGame/LegendOfLegaia'' has Lapis, who has insane attack power and can incapacitate a party member with a string of vicious attacks that deal upwards of 200% of the character's HP. Beating this boss requires either a lot of luck, hours of LevelGrinding, or using a very specific accessory setup. [[note]]Specifically, equipping the Luminous Jewel accessory. Since Lapis's attacks are Light elemental ([[GuideDangIt The game does not mention this.]]), using this accessory cuts his damage output in half and makes his attacks survivable.[[/note]]
* ''VideoGame/SailorMoonAnotherStory'' has [[spoiler:Esmeraude in the fourth chapter]]. Beating said boss gets you [[spoiler:a second Red Pupil]].
* ''VideoGame/MarvelAvengersAlliance'' has the Epic Bosses in certain missions, which only show up if you fight every battle and complete every deploy (which often require spending rare Command Points to recruit specific heroes) in that mission. The bosses offer stronger weapons and gadgets and higher chances of winning more Command Points as prizes for defeating them, compared to normal bosses.
* Even an RPG that is stripped down to its bare mechanics also has one. ''VideoGame/{{Parameters}}'' has the bottom rectangle (previously the second-strongest enemy in the game), which turns into a 9999 hp opponent with high defence and attack after beating the FinalBoss. Thankfully, it isn't really ''that'' difficult so long as you have enough life regeneration, but it does get tedious as it regenerates health quickly and can take a ton of punishment.
* ''Franchise/TheElderScrolls'':
** ''[[VideoGame/TheElderScrollsIIIMorrowind Morrowind]]'' has an AnyoneCanDie nature, so naturally, anyone in the game can be fought and killed. But special mention has to go to [[spoiler: Vivec]]. You are not required to fight or kill him during the main game or either expansion, but if you choose to, you'll have a hell of a fight on your hands. Bonus irony points if you [[spoiler: soul trap him in Azura's Star.]]
*** The Ash Vampires are another example. You only have to fight one in order to get an item off of him, but there are 6 others you can kill. Each one you kill is supposed to weaken [[BigBad Dagoth Ur]] when you fight him, but this does not work due to a glitch in the calculation system. You only need to fight the if you are going for HundredPercentCompletion or for their somewhat useful enchanted items.
** ''[[VideoGame/TheElderScrollsIVOblivion Oblivion]]'' also has a few.
*** Erandur-Vangaril (a lich). He can only be found in a specific cave that none of the game's quests lead you to, and can only be fought there once your character reaches a certain level.
*** The giant slaughterfish, who shows up in one of the dungeons you explore in the Thieves Guild questline, but chances are you won't ever see this one if you don't fully explore the place.
*** There's also the Uderfrykte Matron at Dive Rock.
** The Dragonborn DLC of ''[[VideoGame/TheElderScrollsVSkyrim Skyrim]]'' has the Ebony Warrior, who challenges the player once they reach level 80. His equipment is heavily enchanted, has 50% damage resistance to all elements and can use Dragon Shouts.
*** There are also a few named dragons which are not required to be fought. Of particular note is [[spoiler: Vulthoryol, who can be summed by using the Unrelenting Force shout on the orange globe in Blackreach.]]
* A lot of bosses in any of the ''VideoGame/{{Neptunia}}'' games will be this trope. The strongest in ''VideoGame/HyperdimensionNeptuniaMk2'' is Delphinus without the DLC while a lot of people have a hard time against Gargoyle in ''VideoGame/HyperdimensionNeptuniaV''.
* ''VideoGame/TheLastStory'' has [[spoiler:Therius]] and [[spoiler:Gigamuruk]]. The first is a one-on-one DuelBoss who can only be challenged with Zael alone, in a callback to an earlier boss fight. The latter is fought at the conclusion of the game's running TournamentArc.
* ''VideoGame/TheDenpaMen'' has two. One mid-game dungeon appears to have two bosses--a Water-type Golem and an Ice-type Golem. The Ice-type Golem is [[PathOfMostResistance more difficult to get to, and is the true boss of the dungeon.]] The Water-type Golem, however, gives you a few extra goodies if you beat it. At the very end of the game, you can also choose to fight [[spoiler: The True King, the final form of the King of Evil. He has his own RareRandomDrop, and each time you defeat him, he drops an emblem that can be sold for a [[VendorTrash tidy sum of money]].]]
** The sequel has ''even more'' of these, most of whom are based around chess pieces. Each of the four [[BonusDungeon Caves of Darkness]] contains a different variation on the Knight, and each one is progressively more difficult--especially because the Caves are [[TimedMission timed,]] and even though you can keep battling if you run out of time, if you do, you'll be kicked out of the dungeon before you can collect your rewards for completing it. There's also a Pawn who you have one required fight against early on--but he keeps getting stronger and stronger throughout the game, and you can return to challenge him after different story events. [[spoiler: The last two sets are linked--the "big" BonusDungeon ends with a fight against the Demon Queen, who serves as a combination of this and a TrueFinalBoss. ''This'' unlocks the Bishop, King, and Queen, who fight you back to back in a CallBack to the original game's final boss.]]
* Tyrant in ''{{Opoona}}.'' He can actually be fought surprisingly early on for an example of this trope--before the game's halfway point--and defeating him is required to [[RelationshipValues raise your friendship]] with a few [=NPC=]s. However, taking him on so early and ''surviving'' is another matter entirely.
* ''VideoGame/{{Robopon}}'' has a couple. In the original, you can rematch the first six Legends in Zero Tower post-credits. The second game has several, including Rena's restored-to-youth mother, the younger version of Nick D., the Robopon in Delica Castle's basement, and the W-King.
[[/folder]]

[[folder:Shoot Em Ups]]
* ''VideoGame/{{Gradius}} Gaiden'' has one, in a way. Normally, on Stage 8, you face six bosses, but play it on the second loop of the game to face a seventh: the [[BeamSpam Beam Spammin']] Heaven's Gate.
* Always present in ''VideoGame/{{Touhou}}'' games ever since ''Story of Eastern Wonderland''. The fans would probably riot and destroy Tokyo if ZUN ever released a "proper" Touhou game without one.
** Perfect Cherry Blossom had an ''extra'' Extra Stage with an ''extra'' Extra Boss. She's the one that made Gensokyo. Frightened yet?
** [[LampshadeHanging Lampshaded]] in the 11th game, ''[[GratuitousEnglish Subterranean Animism]]''. When playing as the Marisa/Alice combo, there's a conversation along the lines of: "Why are we here again? We already beat the final boss." "It's the Extra Stage, just do it."
* Finish ''[[VideoGame/{{Parodius}} Gokujou Parodius]]'', and you get to fight your way through a "bonus stage".Who awaits at the end?[[NinjaPirateZombieRobot A fire-spewing laser-shooting warmachine-deploying robotic penguin]].It's as awesome as it sounds.
* ''ArmedPoliceBatrider'' has a crapton of Bonus Bosses, all of which appeared in the ''Mahou Daisakusen'' series and ''VideoGame/BattleGaregga''. Said bosses include Bashinet, the Stage 1 boss of ''Mahou'', and [[ThatOneBoss Black Heart]], the Stage 5 boss of ''Garegga'' that, thanks to the stage edit feature, you can [[WakeUpCallBoss fight as early as Stage 2]].
* ''[[VideoGame/DonPachi DoDonPachi Dai-Fukkatsu]]'' has the first four bosses of ''[[VideoGame/DonPachi DoDonPachi]]'' as bonus midbosses, triggered by fulfilling certain conditions.
* ''VideoGame/{{Hellsinker}}'', as with [[ArmedPoliceBatrider Batrider]] and [[VideoGame/BattleGaregga Garegga]], has loads of secrets. Defeating the Scarlet Queen will result in a secret form of the boss that [[BulletHell unleashes hell]] for 15 seconds, then disappears. The secret form can be easily triggered if the player has the game at a high [[DynamicDifficulty rank]], but it can also cause quite a surprise by randomly appearing under normal circumstances. If that happens, [[http://www.youtube.com/watch?v=X00wKV3SYIE you're in for a world of hurt]].
* ''VideoGame/AbmneshiTheProphecy'' has, in addition to a collection of {{True Final Boss}}es, a secret and entirely optional stage containing Sirisai, who's about as hard as the FinalBoss.
[[/folder]]

[[folder:Simulation Games]]
* The ''Videogame/TraumaCenter'' series has the X operations, which have you performing [[EpilepticTrees simulated/imagined/secret/God-knows-what]] operations involving NintendoHard variations of GUILT, Stigma, or Neo-GUILT.
* Lots of missions in the ''AceCombat'' games feature enemy aces whose defeat is not necessary for mission completion. Unlike traditional examples of the trope they're not really harder than the compulsory aces. On the other hand, there is a more traditional one in [[spoiler: Mobius One and his Raptor]], who would be encountered in an Ace difficulty run of [[BossRush the Gauntlet]] if you did well enough. Similarly are [[spoiler: Scarface One and ZOE Commander]] in a certain ''Skies of Deception'' mission.
* Two of them are available in the combat sequences-filled DatingSim ''VideoGame/MitsumeteKnight'' : [[spoiler: Zeelbis the Bloody]] and [[spoiler: Salishuan the Spy]] of the Eight Generals of Valpha-Valaharian, the main enemy squad of the game. While not a storyline-related boss unlike the other two, [[TheCameo Sparkster]] of the ''RocketKnightAdventures'' series count too.
[[/folder]]

[[folder:Sports Games]]
* ''International Super Star Soccer Deluxe'' for the SNES introduces a bonus match against an All-Star team with perfect stats after you win the World Series. Not only is this team supremely talented, but all your players are tired or very tired.
* In {{Konami}}'s ''NFL Football'' for the SuperNES, you can enter a code to play against the Konami team, who have A+ in all stats.
[[/folder]]

[[folder:Stealth Games]]
* ''VideoGame/MetalGearSolidPeaceWalker'' has the [[spoiler:mock battle with Metal Gear ZEKE.]]
[[/folder]]

[[folder:Survival Horror]]
* Most of the bosses in ''DeadRising'' are Bonus Bosses. And the handful you ''do'' have to fight to complete the game are all ThatOneBoss. The game is ''[[NintendoHard hard]]''.
** Technically you don't have to do any of the bosses. To finish the game you just need to be alive when the time runs out. You only need to do the quests if you want [[MultipleEndings Ending A]].
* ''FatalFrame'' has a particular optional boss only on the Xbox version. A samurai ghost named "Armoured Warrior" who only appears on the final night on the hardest difficulty, who can instantly kill you if he touches you ''AT ALL''. Oh, and he's fully invisible too.
** And he can't be pushed back with a critical shot like every other ghost can be so he's ALWAYS coming towards you without stopping. Again, being invisible, you can't see him but rather HEAR him, unless you get a shot of him fading in and out quickly while looking through the camera, which is the only real way to defeat him.
[[/folder]]

[[folder:Third Person Shooter]]
* ''LostPlanet: Extreme Condition'' features a Bonus Boss, but it's rather unusual. Relatively early in the game, you encounter a giant worm, Akrid, that can CONSUME YOU and takes a [[DamageSponge massive amount of damage]] before falling. You're expected and encouraged to run from it... but if you want the challenge, you can fight and beat it, effectively making it a Bonus Boss. There's even an Achievement for doing so. Later on, you can fight a giant Akrid moth.
[[/folder]]

[[folder:Turn Based Strategy]]
* ''[[VideoGame/FireEmblemTellius Fire Emblem: Radiant Dawn]]'' has Levail, General Zelgius' apprentice. While Ike fights a DuelBoss battle with Zelgius, the rest of your team takes on Levail and his army. Defeating Zelgius is all that you have to do to beat the level, and the rest of your troops don't even have to move, let alone fight Levail (who as a top level Sentinel equipped with the [[BladeOnAStick Wishblade]] is one of the few genuine threats you'll meet in the last quarter of the game). Many choose to engage him though, out of the desire to kill a few more opponents and maybe get their hands on [[InfinityPlusOneSword The Wishblade]].
** Levail's predecessor as wielder of the Wishblade, General Bryce of Daein, is another Optional Boss. Appearing in the last level of the game, Bryce stands in the centre of the map, astride the easiest path to the FinalBoss, Mad King Ashnard. It is however, entirely possible to avoid fighting Bryce by taking another route, although most players don't think to do so.
** In ''[[VideoGame/FireEmblemJugdral Genealogy Of The Holy War]]'', in the Final Chapter, Areone is flying around with a squad of Wyvern Knights. However, the chapter can be cleared without ever fighting him, and he'll even become an NPC ally if Altenna talks to him.
** Strangely enough, [[spoiler: ''Anna'' herself]] serves as this in VideoGame/FireEmblemAwakening's hardest DLC map.
** Outside of DLC, there's Spotpass character [[spoiler:Priam, descendant of Ike]]. His map has you field ''30'' units, which is essentially ''your entire roster'' and one of the highest unit counts in FE ever. [[spoiler:Priam]] himself is equipped with three Breaker skills, Sol, Luna, and nearly maxed stats making him quite a challenge to defeat.
* Demon Supreme Overlord Baal in NipponIchi's ''Marl Kingdom'' series, ''VideoGame/LaPucelle Tactics'', ''Franchise/{{Disgaea}}'', ''VideoGame/PhantomBrave'', ''VideoGame/MakaiKingdom'', and ''Disgaea 2''. In fact, most Nippon Ichi games let you fight characters from their other games as bonus bosses, and they're always at obscene levels. Laharl, Etna, and Flonne from ''VideoGame/DisgaeaHourOfDarkness'' are all Bonus Bosses in ''Videogame/PhantomBrave'', for example. In many cases, defeating them will recruit them into your party. While the final bosses of the games tend to be at level 90-100, the bonus ones usually start somewhere around level ''1000.'' That's ''start'' mind you. In "Etna Mode" of the new ''VideoGame/{{Disgaea|HourOfDarkness}}'' PSP remake, Baal is literally level 9999.
** Mind you, that's not all that impressive. He's actually the third level 9999 boss you've fought by then. He does, though, have about 3 or 4 times the stats of the last one, on an area that randomly clones one character a turn (friend or foe, but clones are all foes), triples all enemy stats, stops all special abilities, and prevents lifting.
** Special mention should go to his Disgaea 3 DLC. Max level, three copies of his Tyrant form (as shown in the page image), well over 400 million HP, and an evility that nulls out damage each round based on how many copies of himself there are on the field. If you don't act quickly enough, the enemy base panels in the back will summon more Baal copies. If you're still too slow, they'll start bringing out Omega Sentinels for the Baal clones to Magichange with. Either you finish it quickly, or otherwise you're screwed.
** ''Franchise/{{Disgaea}}'' adores this function. The final story boss of the game is often one of the absolute weakest enemies the game has to offer. Disgaea 2 had, alone, Overlord Priere at level 500, Marjoly at 1000, Overlord Zenon [[spoiler:(the real one)]] at level 2000, Overlord Baal (the first round) at level 4000, and you still have quite a lot of others. The re-release (mentioned below) also added the DLC characters whom are easy to beat but all sit at 100, and three characters form Disgaea 3 starting at level 500 and ending at level 3500. Additionally, the final boss of Disgaea 2 is level 90 and has no geo effects on the field and is alone. The bonus bosses are often not that gracious, and may have backup, geo effects, and ridiculous levels.
** ''VideoGame/PhantomBrave'' and The re-release of ''VideoGame/{{Disgaea 2|CursedMemories}}'' brought back MythologyGag Pringer X as a BonusBoss, and he's more dangerous than Baal up there for a good reason: he can become immune to any special that's already been used against him, meaning you can't spam the same attack over and over, you HAVE to round out your move set. Later on, you get the chance to fight ''Eight'' of them, and they will all become immune to any special used against one of them, but that's not all: You can later pass a bill that turns all of the Land of Carnage monsters from Uber to Uber Lord, making them not only stronger, but you can't capture them and the bill sticks for that cycle. If you go back to take on Pringer X's army again, their stats are maxed out at 40 million, meaning damaging them is a daunting task in and of itself, much less hitting them.
*** They return in ''VideoGame/{{Disgaea 4| A Promise Unforgotten}}'' as the final bonus boss.
** ''VideoGame/DisgaeaDimension2'' has an incarnation of Baal that is at the moment, the absolute hardest boss NIS has ever made. Most of the examples of this trope in their games can be taken down easily if the player level grinds enough, but Baal in this game, even characters with maxed stats will struggle with him. He never loses a stationary attack bonus, so his damage goes up every turn, switches between some abilities throughout the fight that include summoning clones of him every turn that will rack a ton of damage if you don't kill them, having 50% of all attacks miss, and destroying you base panel and healing himself at the end of ever turn, but throughout the whole fight has Pringer X's ability to become immune to special attacks after they're used on him (though he loses immunity to attacks he was hit with previously when he changes evilities). He has so much HP that it's basically a requirement to raise the stationary attack bonus as high as possible to take him down and even then he's still a MarathonBoss.
* ''LuminousArc2'' has the reoccuring boss for the optional ThatOneSidequest Spa Battle series, [[spoiler:[[LuminousArc Vanessa]]. Not only does she have high strength and can use a stat-boosting spell, she's also joined by respawning and stat-specialised [[MascotMook Kopins]], who only exists to wear down your party. Pity the unfortunate player who didn't bring any anti/nulling fire Lapis and suffers from either her attack, spells or [[LimitBreak Flash Drive]]. She'll get stronger each time you face her, until the sidequest is finished]]. Beating this multiple of times with {{New Game Plus}}es is required for the HundredPercentCompletion.
* ''VideoGame/FinalFantasyTactics'' gave us Elidibs and the Zodiac summon.
* While not really a "Boss" per say, the original AdvanceWars has a bonus Mission after the Final Battle with Sturm called ''Rivals,'' where Eagle challenges Andy to one last go around. In order to access it, you have to play through the Campaign and choose Sami for every Green Earth Mission (barring Eagle's introduction early on of course). This is noted to be quite difficult, as Sami's Green Earth Missions are easily the hardest of them (it doesn't help that she's not nearly the terror that she is in later games either), but it pays off in more ways than one; not only does it give access to ''Rivals'', it also places Eagle as the 3rd CO in the Final Battle, along with an entire squadron of air units to start off (considering the closest airport is neutral and well near the middle, this is a HUGE plus). On the flip side, if you play Rivals in the already [[NintendoHard painful Advanced Campaign]], you're basically doomed to be playing the map for a long time.
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[[folder:Wide Open Sandbox]]
* Both bosses in ''VideoGame/{{Minecraft}}'' are optional. The first is the Enderdragon, which doubles as a final boss. The second, more traditional example, is the Wither, which has to be summoned by completing a difficult task, is ''[[NintendoHard insanely]]'' hard, and drops the Nether Star, which can only be used in constructing Beacons, devices which give you bonus abilities.
* By the same token, nothing in ''VideoGame/DwarfFortress'' says you ''have'' to find the [[TheNotSecret Hidden Fun Stuff]]...
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