History Main / BonusBoss

[[redirect:OptionalBoss]]

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->"''Geez, who started that, anyway? Isn't it enough to have cleared the game in the first place? If there's always an extra dungeon, then the last boss just becomes a midboss!''"
-->-- '''Marisa''', ''VideoGame/TouhouChireidenSubterraneanAnimism'', Extra Stage

The Bonus Boss is a type of OptionalBoss which serves to test players' mettle. They typically aren't directly connected with the main plot of the game, even if their world-ending strength rivals that of the FinalBoss. Sometimes this is justified with an in-universe explanation, but more often than not, it's a glaring example of GiantSpaceFleaFromNowhere, which itself is a subtrope of GameplayAndStorySegregation. Another common nickname for them is "Superboss."

There's no real limit to the number of bonus bosses you can fight; ''VideoGame/FinalFantasyX'' had dozens of them cordoned off in the optional (and highly [[SidetrackedByTheGoldSaucer incongruous]]) MonsterArena. The key features are that defeating one isn't necessary to complete the game, and they require [[OnlySmartPeopleMayPass quite a bit of conscious effort]] to find. Their usual habitat is the end of a BonusDungeon, BrutalBonusLevel, {{sidequest}}, or BossRush. If a late-game boss has multiple difficulty levels, expect the [[HarderThanHard absolute highest]] level to be considered a bonus boss, if not the TrueFinalBoss.

Like any good BossBattle (or FinalExamBoss), when fighting them, it's pretty damn useful to anticipate their actions. It's demanding but strategic. Prizes can include anything from an InfinityPlusOneSword or LastDiscMagic to a simple CosmeticAward. The lure of overcoming an extremely dangerous enemy is enough for [[OneHundredPercentCompletion dedicated players]]; if you're tough enough to beat the strongest boss a game has to offer, you're invincible by that point, and any further upgrades are redundant and only [[BraggingRightsReward for bragging rights]]. The game then picks up from there and just pretends the bonus boss never happened.

Compare and contrast the TrueFinalBoss, which often (but not always) follows and/or replaces the alleged final boss. The former is generally ''not'' an optional encounter [[PointOfNoReturn once the event is triggered]], whereas a Bonus Boss almost always is. You may even earn a GoldenEnding for slaying it, and as icing on the cake, it's usually [[CuttingOffTheBranches the canon ending]].

Contrast SkippableBoss, which is (as the name implies) possible to avoid entirely, but you're probably going to fight it if you took the most intuitive path -- in other words, you didn't try to [[SequenceBreaking Sequence-Break]].

A {{Legacy Boss|Battle}} is a Bonus Bonus that happens to be a character from a previous installment.

A Bonus Boss that drops useful items may lead to UnstableEquilibrium. Compare SecretCharacter for hard-to-find PlayerCharacters.
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!!Examples:

* BonusBoss/RolePlayingGames
** ''BonusBoss/FinalFantasy''
----
[[foldercontrol]]

[[folder:Action-Adventure Games]]
* ''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.
* The ''Franchise/AssassinsCreed'' franchise introduced bonus bosses starting with ''VideoGame/AssassinsCreedIVBlackFlag''. Defeating them usually comes with valuable rewards like large sums of money, special abilities, and most often [[InfinityPlusOneSword top-tier equipment]], but some reward nothing but personal satisfaction and [[BraggingRightsReward bragging rights]].
** In ''VideoGame/AssassinsCreedIVBlackFlag,'' there are five legendary ships that you can fight in any of the four corners of the map: The [[LongRangeFighter HMS Prince]], who will pester you from afar with mortar shots, [[NighInvulnerability La Dama Negra]], who can only be fired at from behind, The [[DualBoss HMS Fearless]] and The [[DualBoss Royal Sovereign]], who will surround and double-team you, and the [[ThatOneBoss infamous]] [[LightningBruiser El Impoluto]], who uses her greater speed and maneuverability to ram your elite hull armor to oblivion. You win 20,000 Reales for winning each fight, but by that point you've probably bought all the ship upgrades you needed to actually beat them, so it's more of a BraggingRightsReward. Defeating all five ships gives the ''Jackdaw'' the ''El Impoluto'''s boosted ram attack, but then again, by that point there's not much left to use it on.
** ''VideoGame/AssassinsCreedRogue'', being something of a MissionPackSequel to ''Black Flag'', copies the latter's four legendary ship battles, only this time it's against entire fleets led by a souped-up flagship. Thankfully you get an AI fleet of your own as backup, but you'll still be doing most of the heavy lifting. Winning all four battles then unlocks the real superboss, the ''Storm Fortress'', flagship of the Assassin fleet and an insanely powerful Man o' War that's fought amidst a raging thunderstorm. When its health drops to about 30% it summons backup in the form of two additional level 70 Man o' Wars that fight exactly like the [[DualBoss HMS Fearless and Royal Sovereign]] mentioned above.
** ''VideoGame/AssassinsCreedOrigins'' lets you fight gigantic manifestations of various Ancient Egyptian gods like Anubis or Sobek. They're [[StationaryBoss Stationary Bosses]] that can only be defeated by pelting them with arrows from afar while dodging their powerful attacks. Uniquely in the franchise, their existence is implausible even by this universe's standards, so they're explained away as AGlitchInTheMatrix caused by corrupted Animus data.
** ''VideoGame/AssassinsCreedOdyssey'' has a huge number of bonus bosses drawn from Ancient Greek mythology, ranging from eight legendary animals to cyclopses, the Minotaur, the Sphinx, and even a bunch of Greek gods up to and including Hades himself. However, the definition of what counts as a BonusBoss is a bit murky in this installment due to its multiple independent story arcs, many of which are tied to DownloadableContent. For instance, the mythical monsters like the Minotaur are bonus bosses in the main game but mandatory for the DLC arcs that lead to the game's true final ending.
** ''VideoGame/AssassinsCreedValhalla'' takes what ''Odyssey'' perfected and transplants it into Norse and Celtic mythology, interspersed with a bunch of powerful human bosses that're part of sidequests.
* ''VideoGame/BloodstainedRitualOfTheNight'': All of the Bonus Bosses in this game are manifestly more difficult than the final boss if fought normally.
** Finding the Carpenter's Key unlocks a fight with the Master Carpenter.
** Finding the Millionaire's Key unlocks a fight with Millionaire's Bane, a possessed slot machine.
** Finding the Warhorse Key unlocks a fight with Revenant, an {{Expy}} of [[VideoGame/CastlevaniaRondoOfBlood Richter Belmont]].
** Once you reveal 99% of the map, O.D. will have a new book available in the library called the Tome of Conquest that he will point out is especially valuable. If you take it with you into the final area, he will fight you for it. If you beat him, you can borrow all of his books at once.
** Anyone who purchases the Website/{{Kickstarter}} Edition of the game gets to challenge an extremely difficult [[CreatorCameo secret boss]] for a shot at acquiring the [[WhipSword Swordwhip]].
* ''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.
** 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. ''Portrait of Ruin'' also has the Nest of Evil, a bonus painting that contains many bosses, mostly ones from ''Dawn of Sorrow'', and then the Doppleganger.
** ''VideoGame/CastlevaniaLamentOfInnocence'' has The Forgotten One, a [[ColossusClimb giant]], 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/DoctorLautrecAndTheForgottenKnights'': Completing every quest including the ones after the main story unlocks a last dungeon to encounter a Treasure Animatus that's on par with the last form of the final boss.
* ''VideoGame/DragonsDogma'' has a few superbosses, including:
** The Ur-Dragon, a {{Dracolich}} that can be fought in the postgame. In comparison to the Dragon fought before the postgame, the Ur-Dragon is a DamageSpongeBoss ''par excellence'', such that it is not meant to be defeated in one go, or even by just one player: when connected to the game's online servers, the Ur-Dragon's HP is shared across all players' games. When fought in offline mode, the Ur-Dragon's HP is reduced to a more reasonable level, but even then it is very hardy.
** The ''Dark Arisen'' expansion includes [[GrimReaper Death]] as a repeating boss encounter on Bitterblack Isle. It, too, is a DamageSpongeBoss that will retreat after a certain point (its HP carries over into subsequent encounters), and true to its name, even a glancing blow from its scythe spells [[OneHitKill instant death]]. This can be particularly troublesome for Pawns, as getting hit by Death's scythe will immediately send them back to the Rift without a chance to revive them.
* ''VideoGame/GodOfWarPS4'' has the Valkyries, who are among the toughest enemies of the games with each having a unique attack. After you defeat them all, you can challenge their queen Sigrun, who is not only stronger but has all of their attacks.
* ''VideoGame/HollowKnight'' unlocks a large number of optional bosses once you acquire the Dream Nail, some distinctly more difficult than others. The Warrior Dreams encountered at ceremonial gravesites and fought on the main map talk tough but are relatively easy to defeat, and defeating a few of these for their Essence is practically mandatory to achieve the good ending. The upgraded versions of normal bosses killed ''by the player'' and refought in off-the-map pocket dimensions, however, generally exceed the normal FinalBoss in difficulty; several of these do double damage with every single attack. This especially applies to the bosses added by the content packs: ''Hidden Dreams'' added several increasingly hard versions of White Defender (Dung Defender) and Grey Prince Zote (whose normal incarnation is the easiest boss), and the BossBonanza added in ''Godmaster'' has similarly upgraded versions of every single BossBattle in the game.
* ''VideoGame/IllusionOfGaia'' has Solid Arm, [[LegacyBossBattle 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/IttleDew1'' has one at the end of the [[BonusDungeon Master Cave]]. Oddly, it's the one boss you beat through brute force rather than [[PuzzleBoss some kind of puzzle]].
* ''Franchise/TheLegendOfZelda'':
** ''VideoGame/TheLegendOfZeldaALinkToThePast'':
*** The Four Sword Links in the remake on the UsefulNotes/GameBoyAdvance. 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 (though it did lead to a new ending).
*** In the remake, Helmasaur King is a Mini-Boss in the Palace of the Four Sword. This one is more durable and it can regenerate its mask; what's more, it can summon Helmasaurs to impede Link, has to be hit with a Light Arrow before Link can strike it with his sword.
*** Arrghus is another Mini-Boss from the Palace of the Four Sword. This one replaces the Arrgi with regular Bari (that instantly electrify themselves once they get hit with the Hookshot), and summons Kyamerons in its second phase.
*** Mothula is the third Mini-Boss in the Palace of the Four Sword. This one is much faster, has a Doppleganger Spin, and can summon bees to attack.
*** Blind the Thief is the fourth Mini-Boss of the Palace of the Four Sword. With a side bit of PuzzleBoss: whenever it gets decapitated, Link must swat the head back to its own body to make Blind vulnerable again.
** 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.
** ''VideoGame/TheLegendOfZeldaALinkBetweenWorlds'': Once you've completed all the [=StreetPass=] challenges, you're able to fight the bonus boss of that game. [[spoiler:It's Gramps, the curator of these [=StreetPass=] challenges. He originally set them up just so he can find and fight someone stronger than him.]]
** ''VideoGame/TheLegendOfZeldaBreathOfTheWild'':
*** Lynels [[BossInMookClothing aren't even considered bosses by the game]], but every fight with one is difficult. You are only ever needed to encountered one once in the game, and even then you are not required to beat it (and can even skip it entirely if you find another way to obtain Lightning Arrows). They are the most difficult reoccurring [[BossInMookClothing basic enemy]] in the game, and for a while the most powerful variant, the [[LawOfChromaticSuperiority Silver Lynel]] (who has more health than the ''final boss'' of the game) can only be encountered in the half-destroyed Coliseum, before other Lynels start to [[LevelScaling scale up to Silvers]]. [[HarderThanHard Master Mode]] of the game introduces an even stronger version of the Lynel, the [[GoldColoredSuperiority Golden Lynel]]!
*** The Champions' Ballad DLC is an involved quest administered by one of the Sheikah monks, mirroring your journey in the main game by adding new trials to the key areas on the map. After going around Hyrule and completing several tests, a new dungeon opens up. [[spoiler: The monk, Maz Koshia is at the end, and looks like any of the other inanimate mummified monks, giving the typical speech once Link reaches the end of a shrine. But then he starts ''moving'', tells you he has a final test, and teleports you both into a boss arena--he is your opponent. Maz Koshia turns out to be the most challenging boss in the game (more than ''[[FinalBoss Calamity Ganon]]''), borrowing from many previous bosses and tough enemies while adding tricks of his own. For a shriveled mummy, he's pretty strong, with a lot of health, hard-hitting attacks, and multiple phases that keep you constantly on your feet. Hearts, armor, food buffs, and the upgrades to your Champion powers obtained during the DLC certainly help, but even so, they still don't make him easy.]]
* ''VideoGame/{{Okami}}'' has the [[spoiler:Bandit Spiders and the Kusa Five]].
* ''VideoGame/TribalHunter'' has 4 spread out over the latter half of the game:
** Laura, who you find at the end of a passage way in the Jungle filled with ko'd pirates.
** Wave, who you meet in the Hive in a not so hidden passage that ends in a room with him and a bunch of boxes and chests.
** The Queen Bee, who's arena is to the right of the exit to the mountain top.
** And The Alpha, who's arena is in the mountain top area, it's entrance in the same room as where you first find the wolf enemies.
[[/folder]]

[[folder:Action Games]]
* In ''VideoGame/ActRaiser 2'', enter the password "Xxxx Yyyy Zzzz" to fight the final boss from the first game with the second game's mechanics, who [[NintendoHard takes several steps up in difficulty]] from the first game, as well as the final boss from the second.
* ''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.
* ''VideoGame/MetroidOtherM'' has the ''Franchise/{{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. For technical reasons (namely the absence of items and thus the impossibility of a PlayableEpilogue), the Phantoon fight was intentionally left out of Hard Mode.]]
[[/folder]]

[[folder:Beat 'em Ups]]
* Via ''VideoGame/AsurasWrath'' DLC, two Bonus Bosses that have nothing to do with the main game story are [[Franchise/StreetFighter Ryu and Akuma]], who become Evil Ryu and Oni respectively.
* ''VideoGame/{{Bayonetta}}'':
** Rodin 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.]]
** Beating all Alfheim challenges unlocks [[BrutalBonusLevel Angel Slayer,]] with a boss fight against another Bayonetta. Mechanically she's similar to [[MirrorBoss Jeanne,]] but with more health. Like Rodin, she must be fought at the highest difficulty, due to how difficulty in Angel Slayer progresses on Verse instead of being set by the player.
* ''VideoGame/Bayonetta2'':
** Rodin makes a return, this time available if the player buys the Platinum Ticket for a staggering 9,999,999 halos. Unlike his encounter in the first game, you can use [[BulletTime Witch Time]] against him, since Infinite Climax difficulty no longer disables that feature, but beyond that, Rodin is even harder this go around, especially since you start fighting him in his normal form, before he TurnsRed and becomes [[OurDemonsAreDifferent The Infinite One]].
** The BrutalBonusLevel of this game, the Witch Trials, ends with two DualBoss rounds. The penultimate verse is against Bayonetta and Jeanne, and the final verse is against Balder and Rosa. Three out of four of them were not fought in the game's single player campaign. [[spoiler:Balder is the only one that was, known for most of the game as the Masked Lumen.]]
** Tag Climax has secret stages that have a random chance of appearing. Most of them are of the other player characters, but there is also one against Bayonetta's demon summon Labolas.
* The Red Dragon features as a Bonus Boss in both of the ''VideoGame/DungeonsAndDragons'' {{Beat Em Up}}s.
* The doujin game ''VideoGame/GriefSyndrome'' 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]].
* ''VideoGame/NoMoreHeroes2DesperateStruggle'' has Kimmy, a school girl with an [[{{Yandere}} unhealthy obsession over Travis]]. You only fight her if you don't go back to the Motel between fights with Charlie and Matt, making her the only assassin in the series who truly fits this Trope.
* 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 [[SkippableBoss 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]].
* In ''VideoGame/SenranKagura (Burst)'', after defeating the final boss, you have the opportunity to fight a sixth playable character for your chosen faction [[spoiler:(Daidoji for Hanzo Academy, and Rin for Hebijo Academy)]]. In order to win the mission and [[DefeatMeansPlayable make them playable]], you have to defeat the boss with all five of your other characters in succession, without losing.
* ''VideoGame/{{Yakuza}}'':
** The series has Jo Amon and the other members of the Amon Clan appear as the ultimate boss in every game, including the spinoffs. For most of them, you can only fight them after completing every other substory in the game.
** There's also the Mr. Shakedowns in ''VideoGame/Yakuza0'', a quartet of massive [[BossInMooksClothing Bosses In Mook's Clothing]] who wander the map and can massacre Kiryu and Majima in a couple hits and then take all their money. Unlike the Amon Clan, who can't be fought until near the end of the game, the Mr. Shakedowns start appearing near the start, and without lots of skill, plenty of leveling or just knowledge of their weaknesses it's suicide to take them on.
** Virtually every main game in the series has a coliseum where you can fight various enemies that you can't fight otherwise, including members of the aformentioned Amon clan, other protagonists, the masters who trained you, [[BreadEggsMilkSquick bears and tigers]], and [[CelebrityCameo real-life professional wrestlers]].
[[/folder]]

[[folder:Card Games]]
* ''VideoGame/YuGiOhReshefOfDestruction'':
** The game has the Hall of Eternity, where you can battle Yami Yugi, Yami Marik, Yami Bakura, Dark Joey/Jounouchi, Noah Kaiba, Pegasus, Shadi, and Paradox.
** There are also three optional fights. If you visit Italy at a specific part of the game, you'll duel Jean-Claude Magnum a second time, who has a better deck than the first time. Second, at another part of the game, Tea is standing at the town square. If you talk to her, you'll have to deal with Johnny Stepps and then Krump, one after another.
* ''[[VideoGame/YuGiOhTagForceSeries Yu-Gi-Oh! GX Tag Force Evolution / The Beginning of Destiny]]'': After beating the game at least 5 times with 5 different tag partners, go to the Card Shop at daytime, you can now challenge Sadie (who previously states she doesn't know how to play), she's now using a very powerful lockdown-burn deck, which makes her far more powerful than any other NPC.
* In ''Yu-Gi-Oh GX Duel Academy'' there is an event where you can challenge and duel Pharaoh, Dr. Banner's cat. To do so, you must be a member of the Slifer dorm, and have defeated Jaden, Syrus, Chumley and Banner three times each. If you then talk to Banner on a Saturday, you can duel Pharaoh, and get a card afterwards. (Panther Warrior for winning, Bone Mouse for losing, and Outstanding Dog Marron for drawing).
[[/folder]]

[[folder:Fighting Games]]
* ''Franchise/BlazBlue'':
** ''VideoGame/BlazBlueCalamityTrigger'' 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 (the TrueFinalBoss method). ''[[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.
** ''[[VideoGame/BlazBlueContinuumShift Continuum Shift: Extend]]'' added Unlimited Mars mode, which is essentially a gauntlet of bonus bosses. It's a straight run of ten characters, but all in their Unlimited versions which have buffed stats and crazy new move properties/moves. ''[[VideoGame/BlazBlueCentralFiction Central Fiction]]'' replaced this with Grim of the Abyss mode, which is effectively the same thing.
* ''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.
* Uranus made her debut in ''[[VideoGame/BloodyRoar Bloody Roar 3]]''. To reach her, the player must win every fight without losing a single round; which includes the fight against [[TrueFinalBoss Xion.]] If successful, Uranus will appear immediately afterward, however, this also represents the PointOfNoContinues. Meaning, if you lose, it's an automatic GameOver. So you only get one chance to ''try to'' defeat '''''[[GameBreaker one of the most broken fighting game characters EVER.]]'''''
* ''[[VideoGame/CapcomVsSNK2MarkOfTheMillennium Capcom vs. SNK 2]]''. Bison and Geese (chosen randomly). Originally the main bosses from its previous installment, they will interrupt you before heading to the final match without any cutscene. To face them you must have at least 800 GP, never let your opponent achieve 5 First Hits, and finish at least 2 matches with a Custom Combo or Super Combo finish. Defeating them is one of the requirements in order to face [[TrueFinalBoss The True Final Match]] after your next match.
** ''VideoGame/SNKVsCapcomSVCChaos'' has [[VideoGame/{{Athena}} Princess Athena]] and [[VideoGame/GhostsNGoblins Red Arremer/Firebrand]].
* ''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, ''VideoGame/FatalFury Special'' had a Bonus Boss 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''.
* 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's new more-than-max-level OneWingedAngel, Feral Chaos. Your reward for beating him? The ability to play him.
* Baiken, in the original ''VideoGame/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.
** ''Slash'' and ''Accent Core'' also added in Order Sol, a past version of protagonist Sol Badguy, as one too. Fighting him in the latter requires having half of your victories (depending on the number of rounds set) be Overdrive/Instant Kill finishes before facing I-No; after which she will then teleport them to the past to fight him, which will no doubt end poorly considering how [[SNKBoss overpowered he is]]. Fortunately, unlike Baiken above, Order Sol is available to use from the start so you don't have to subject yourself to such cruelty to get him.
* If you manage to beat ''[[VideoGame/TheKingOfFighters The King of Fighters: Maximum Impact Regulation A]]'' without using any continues and with enough Super Finishes, you'll get to fight [[GuestFighter Makoto Mizoguchi]] of ''VideoGame/FightersHistory'' fame.
* ''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.
* ''Franchise/MortalKombat'' is the TropeMaker:
** The [[VideoGame/MortalKombat1 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 [[CreatorCameo Dan Forden]] appear and say "TOASTY!" while fighting on the Portal stage, then hit 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 Mortal Kombat 3'' added Mileena, Ermac, Classic Sub-Zero, and Human Smoke. ''Mortal Kombat Trilogy'' added Chameleon and Khameleon, who were 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.
* ''VideoGame/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.
* In ''VideoGame/Persona4Arena'', it's possible to unlock a special bonus match against [[spoiler:Elizabeth from ''VideoGame/Persona3'']]. 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.
* ''VideoGame/PunchOut'':
** The Wii game has Franchise/DonkeyKong. He can only be encountered during the final segment of Story Mode (Mac's Last Stand), and it's not required to defeat him as the game only truly ends with [[spoiler:Mac's retirement from boxing]] after three defeats (in fact, merely facing DK once is enough to have him available in Exhibition Mode).
** ''Super Punch-Out'' for the SNES has the boxers of Special Circuit (led by Nick Bruiser, the TrueFinalBoss); the circuit itself has to be unlocked by winning the first three circuits (Minor, Major and World) without suffering a single defeat.
* ''VideoGame/SamuraiShodown 2'' had a very tough Bonus Boss in Kuroko, whom you could either fight by meeting certain conditions, or just randomly after stage 3.
* In ''VideoGame/SoulCaliburIII'', 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.
* ''Franchise/StreetFighter'':
** Akuma is usually a bonus boss in the games where he isn't the TrueFinalBoss, particularly in ''[[VideoGame/StreetFighterII 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.
* ''[[VideoGame/{{SUGURI}} Acceleration Of SUGURI X-Edition]]'' has Sora, the protagonist of [[VideoGame/{{sora}} her own game]], who can be unlocked by playing the Arcade Mode in Normal or Hard without using continues, and if you did well enough to fight Hime in the Moonlight stage, and keep your ranking consistently in A; defeat her and she's yours. However, if you do well enough to keep a ranking of S, you get to fight Robo instead.
* ''VideoGame/SuperSmashBros'':
** ''[[VideoGame/SuperSmashBrosMelee 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 ''[[VideoGame/SuperSmashBrosBrawl Brawl]]'', extra doors appear in three stages after you beat Tabuu; going inside them will pit you against Toon Link, 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.
** In all games from ''Melee'' onward, Crazy Hand will join Master Hand as the final boss of Classic Mode if the player can get up the ladder fast enough while playing on a specific difficulty.
** In ''[[VideoGame/SuperSmashBrosForNintendo3DSAndWiiU Smash 4]]'', if the player is playing on a difficulty 3.0 or higher, your final opponent will be both Master Hand and Crazy Hand, however things get weird from here. If the player is on 5.1 or higher, they will be surprised when Master Hand and Crazy Hand blast apart, forming the various forms of Master Core. on 5.1, they will be attacked by Master Edges, at 6.0 they will get fought by Master Beast, then Master Edges. At 7.0, first Master Giant, then Beast, then Edges. No matter which difficulty, after beating the forms, you will then face Master Shadow, a duplicate of your current character. Finally, if you're on the Wii-U version and are playing at 8.0 or higher, you will then be attacked by Master Fortress, which is essentially a living stage requiring you to defeat four weakpoints while being accosted by various enemies. After all of that is done, Master Core will reveal itself, and if not defeated in under a minute, will instantly K.O. the player if they fail to dodge its attack. If the player defeats the orb or survives the attack (either by dodging or having more lives) then the battle is ''finally'' over.
* ''VideoGame/{{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 ''Tekken 6'', there's Nancy. She's one of several [[HumongousMecha giant robots]] developed by the Mishima Zaibatsu, perhaps to combat [[BigBad Azazel]], who [[Series/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.]]
* ''Vampire Savior'' has Oboro Bishamon, the man himself, rather than the armor. ''VideoGame/{{Darkstalkers}} 3'' makes him playable.
* 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.
* ''VideoGame/WakuWaku7'' and ''Galaxy Fight'', the two fighting games made by Creator/{{Sunsoft}} for the UsefulNotes/NeoGeo, shared a common bonus boss named "Bonus-Kun", a punching bag (from "[[PlanetOfHats the Punching Bag Planet]]") with a limited moveset who parodies [[Franchise/StreetFighter Ryu]]. In ''Galaxy Fight'', [[DidYouJustPunchOutCthulhu after you defeat Felden]], you get to fight a final Bonus Boss in the form of Rouwe, an old man dressed in a karate gi.
* ''VideoGame/WayOfTheWarrior'' has a hidden contender named Gulab Jamen who [[DemonicPossession possesses]] three existing characters in the roster to fight you if you achieve special conditions. Dragon becomes ''Black'' Dragon, Fox becomes Voodoo, and Major Gaines becomes Major Trouble. Once they're all out of the way, Gulab can be fought on his own.
[[/folder]]

[[folder:First-Person Shooter]]
* ''VideoGame/Borderlands1'' has some in the optional side quests, some of which, like Mothrakk and Marley & Moe, can reach ThatOneBoss status. The ''true'' Bonus Boss doesn't come until you've downloaded and finished ''The Secret Armory of General Knoxx''. That unlocks a fight against Crawmerax the Invincible. 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/Borderlands2'' 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)"]]''' Terramorphous' health value on Overpower 10 difficulty is 65,762,390,016.
** 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 Vermivorous The Invincible]]. Vermi is easily the most annoying boss to spawn in-game. Thankfully, Vermi is not very healthy for being a raid boss. She only has 12,971,369,472 health on Overpower 10. For comparison, the pod that she comes out of has just 2,849,703,424 health on Overpower 10.
** Hyperius the Invincible, a mutated, power-mad Hyperion engineer found in the ''Captain Scarlett and Her Pirate's Booty'' DLC. Hyperius' health value is 30,320,844,800 on Overpower 10. His health value does not increase when there are more players in your session because he is set for four-player difficulty all the time.
** Master Gee the Invincible, a PuzzleBoss from the same DLC, and his horde of sand worms (who will avoid the player if they're in Fight For Your Life). Gee's health and shield values are 402,794,610,688 health and 20,139,730,944 shields on Overpower 10. Just like Hyperius, Gee's health value does not increase when there are more players in your session because he is set for four-player difficulty all the time.
** ''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''. Pete is the least difficult of the raid bosses, only having 39,120,728,064 health and 34,389757,952 shields on Overpower 10.
** ''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. Vorac has 51,787,878,400 health and 11,037,966,336 shields on Overpower 10.
** Dexiduous the Invincible, A '''''secret''''' secret boss from the same DLC, a colossal [[BigCreepyCrawlies drifter]], is the single largest enemy in the series. It costs over 100 Iridium to summon, and even then, you have to fight trough hordes of Badass and '''''Super Badass''''' enemies before it will even appear. It can only be damaged by hitting it's critical spots, and it has HP in the '''''TRILLIONS.''''' His actual health value on Overpower 10 is 6,485,684,781,056. Let me repeat that. [[PunctuatedForEmphasis Six. Trillion. Health.]] As if that weren't enough, on four-player difficulty, [[FromBadToWorse Dexi has 25,942,739,124,224 health]].
** ''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. Since this particular raid has a focus on fighting four raids at once, their health is spread around sort of equally. As an added bonus, each dragon has their own gimmick.
** Brood [[MookMaker can spawn Green Basilisks which make for easy Second Winds]]. He has 11,225,223,168 health on Overpower 10.
** Boost raises the level of the other dragons by 1 each time he lands. He has just 7,483,482,624 health on Overpower 10.
** Incinerator has a channeled area-of-effect attack, during which he reflects all attacks and can make parts of the arena erupt in fire. He has 14,966,965248 health on Overpower 10.
** Healianth can restore the health of the other dragons, and has the highest health value of the dragons. He has 22,450,446,336 health on Overpower 10.
** The fifth Headhunter DLC, ''Sir Hammerlock vs. the Son of Crawmerax'', adds one raid boss in the form of the colossal craboid, The Invincible Son of Crawmerax the Invincible. Crawmerax actually the least health of all the raid bosses in Borderlands 2, sitting at just 11,674,231,808 health on Overpower 10.
** The fifth story DLC, ''Commander Lilith & the Fight for Sanctuary'', adds one last raid boss in the form of Haderax the Invincible. Haderax is a giant, purple Sand Worm. He has a staggering 78,914,863,104 health on Overpower 10.
* ''VideoGame/BorderlandsThePreSequel'' also includes a few bonus bosses. Once the main storyline is beaten, the player can fight an upgraded version of the final boss, the Invincible Sentinel. This gets bonus points for explicitly being non-canon; Tina and Brick wanted to hear about Athena fighting a raid boss, so they had her make one up. There is also a hidden bonus boss that the game doesn't tell you about, a giant rock monster named Iwajira (though once you know how to get to there, it is pretty easy to find).
* ''VideoGame/MegaMan8BitDeathmatch'' has several in the single player mode:
** The original version from the beginning had [[spoiler:the three Mega Man Killers]], who you could fight if you could beat Flash Man's, Drill Man's, or Knight Man's stages quick enough. You only had one chance to beat them, but if you were successful, you would earn their weapon for the rest of the current chapter you were playing. [[spoiler: Oh, and the game remembers that you had beaten them, as they appear in a room before the BossRush in [=V5B=] onwards.]]
** In v5, if you [[spoiler:defeat Bass in the ''VideoGame/MegaMan7'' chapter without using the Super Adaptor]], you'll be able to fight [[spoiler:the Wily Capsule, the [[DemotedToExtra original chapter 7 boss that Bass replaced]]]].
** Also in v5, [[spoiler:Quint]]. To even find him, [[spoiler:you had to have beaten up to Chapter 11, and then afterwards, back at Dr. Light's lab, you had to go to the training area to get a weapon capable of boosting your height in whatever way, such as the Tornado Hold or Super Adaptor. With that weapon, you then had to go to the pond with the waterfalls outside and then use that weapon to reach the waterfall opening above]]. The fight itself is by far the hardest boss in the game, possessing powerful attacks very capable of eliminating your life meter, and with ''[[MarathonBoss five gruelling phases]]'' to boot with [[CheckpointStarvation no checkpoints at all if you die at any point]]. To say nothing of its spectacle: [[spoiler:First, Quint fights you in a strange location in the middle of a time void, and then he takes you to a prehistoric like arena with lava flowing down the middle. After that, you end up in [[VideoGame/MegaMan10 Solar Man's stage]] with the arena consisting of conveyor belts surrounded by lava. Then he takes you to the highway from the beginning of the first ''VideoGame/MegaManX1'' game, complete with Road Attackers appearing during the fight. Finally, you end up back in the time void area from the beginning of the fight, except you're up against '''''two''''' Quints fighting you]]. The reward you get for beating him? [[BraggingRightsReward A trophy appearing in the basement of Dr. Light's lab]].
** v6 added [[spoiler:Ra Thor and Ra Devil]] in Chapter 13. After finding all the artifacts for Pharaoh Man's sidequest ([[GuideDangIt good luck with that]]) and making your way through a gauntlet of puzzles, [[spoiler:you find Ra Moon, who then activates and drops Ra Thor on you, followed by Ra Devil if you manage to beat Thor. Both have ''very'' high HP, and Devil becomes invincible at three different points of the fight to [[PuzzleBoss put you through deadlier versions of the puzzles you solved to get to it.]]]] Defeating them gives you the [[spoiler:Dawn Breaker]], a chapter-exclusive InfinityPlusOneSword.
[[/folder]]

[[folder:Hack and Slash]]
* ''VideoGame/DiabloII'' 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 an "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!
* ''VideoGame/DiabloIII'' 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 four such battles: Maghda and the Skeleton King, Ghom and Rakanoth, Zoltun Kulle and the Siege Breaker Assault Beast, and Uber Diablo who can clone himself and summon two of the other ubers. There is a special reward for winning all four battles and collecting special rare items from them.
* ''VideoGame/DungeonSiege'' 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]].
* ''VideoGame/GrimDawn'' has the bosses of the four challenge dungeons, each found at the end of a long multi-level dungeon that must be cleared in one run without dying. There are also the Nemesis bosses, who only start spawning once you have maxed out your infamy with their respective faction. All of the above have exclusive Monster Infrequent items only they can drop.
* 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.
* ''VideoGame/PathOfExile'' added several of these over the years:
** Queen Atziri was the first Bonus Boss added to the game. To reach her domain, you need all four Vaal fragments, which are typically located in corrupted zones that appear occasionally, and not guaranteed. Defeating her nets one of her exclusive uniques and a chance to get a piece of an advanced Vaal fragment, which unlocked an even ''harder'' version of Atziri, who drops some of the best unique items in the game.
** Izaro lies in [[MarathonLevel the Labyrinth]]. He hits hard and is always assisted by his Goddess who attacks independently from him. He's fought in three stages. The first two adds a gimmick that changes daily and need to be dealt with if you don't want it to carry over to the next phase and the last phase is in a room filled with traps. Defeating him earns you the ever-important [[PrestigeClass Ascendancy class]] skill points. Also inside the Labyrinth is a Bonus Mini-Boss, Izaro's pet Argus.
** The ''Atlas of Worlds'' added a final boss for the post-game map content, the Shaper, who was guarded by four other difficult boss fights located in the highest tier maps in the game. Then, a TrueFinalBoss of the Atlas got added, a DuelBoss with the Shaper and the Elder, who required defeating both bosses and then spreading the Elder's influence to the Shaper's realm and fight through both their guardians. In ''Conquerors of the Atlas'', Sirus, Awakener of Worlds, replaces him as the final Atlas boss, and ''Echos of the Atlas'' added a second seperate final boss, the Maven. The Shaper and the Elder can still be fought by collecting fragments from influenced maps.
** Many seasonal leagues added a handful of Bonus Bosses over the years, and the list continues to grow. Most of them aren't TemporaryOnlineContent, however, since most of them have been reintroduced into the game after their respective league as part of the game's core content.
* Used in a rather creative way in ''VideoGame/SevenSamurai20XX'': The third chapter features a whole, confusing city to explore, and before the series of events leading to the last boss fight that will end the level, you can encounter a series of unique NPC which can be challenged and fought as bosses in various parts of the city, namely Pyro (a guitarrist with a garish green outfit and pink afro), Morozumi (a sexy black woman covered in bandages and using kunai), Tsubaki Dayu (a graceful masked woman warrior), Gotehnmaru (a warrior in a nice suit), Oniwaka (a massive man in a kendo suit), Ushiwaka (A ninja-like swordsman) and finally Brahman (a magician-like fighter who can turn invisible). Defeating them has no impact on the plot, but once you finish the game they unlock the Arena Mode where you can fight against all previous bosses.
[[/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.
* ''VideoGame/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/DragonNest'' has several high level maps feature alternative routes with different bosses.
* ''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 has such [[https://www.reddit.com/r/ffxiv/comments/apld7n/absolute_virtue_what_ffxiv_players_should_know/ absolutely obscure]] mechanics that it was never beaten fairly until the rising level {{cap}} made it irrelevant.
* ''VideoGame/FinalFantasyXIV'':
** The game features plenty of end-game contents, some of which are either BonusDungeon while others are this, or both. Some of the content is loosely tied with the overall plot; completing them isn't necessary to advance the story. Hard Mode and Extreme Mode versions of the Primal fights are available to tackle, along with the bosses in the intermediate 24-man, and hardcore 8-man, raids, with the latter having a Savage version which brings more mechanics to challenge the team.
** ''The Unending Coil of Bahamut'' takes the cake as the first raid content to be pegged at the '''Ultimate''' difficulty. And it certainly doesn't disappoint, as it consists of embellished and fiercer version of the final turn for each part of the Binding Coils of Bahamut (Turn 5, 9 and 13), with all of them [[TurnsRed pulling all their stops at the get-go compared to regular Coil]], culminating with Bahamut Prime dropping [[ColonyDrop a mini-Dalamud]] to the stage and sends powerful shockwaves that will wipe the party if not mitigated with a Limit Break from a tank-role player. And then after the Tera Flare phase, Bahamut Prime proceeds to [[TurnsRed unleash its inner rage]] in its golden form, and starts to spam Akh Morn and Exaflare, and if it was not defeated quickly it will begin to spam Morn Afah (appropriately means "eternal death" in dragon language) until the whole party is wiped out. Clearing the Unending Coil demands a great amount of team synergy and their proficiency with the battle mechanics much more than any other raids before it, to the point that Deltascape 4.0 Savage (the highest-level raid content when Unending Coil was released) is a mandatory requirement ''just to enter it''. Furthermore, at the time of its release, none of the participants were able to clear it within the first week, with the world first clear happens on the 11th day after the release.
** The Weapon's Refrain is just as difficult. Just like the Unending Coil, this fight is a gauntlet against several bosses in a row; Specifically: Garuda, Ifrit, Titan, Lahabrea, and the Ultima Weapon. In addition to the moves they usually do being supercharged, the whole encounter is a [[PuzzleBoss giant puzzle]], as the party needs to ''[[ViolationOfCommonSense hit the Primals with their own attacks to power them up]]'' in order to obtain extra {{Limit Break}}s for use against Lahabrea, and failing to do so will ''always'' result in a wipe. A Level 3 Caster Limit Break is required to destroy several [[ActionBomb self-destructing Magitek Bits]] before they explode, a Level 3 Healer Limit Break is needed to cleanse an otherwise uncleansable Doom debuff Lahabrea places on the party, a Level 3 Melee Limit Break is needed to finish off Lahabrea before he casts Dark IV to wipe the party, and a Level 3 Tank Limit Break is needed to survive the Ultima Weapon's opening attack of Ultima. Then, once the Ultima Weapon fight begins proper, ''dying to it causes it to build up its own Limit Break faster''. If the Ultima Weapon reaches 100% charge, it begins dragging players one at a time into the air and blasting them with an attack that deals 999,999 damage ''and prevents their corpses from being targeted, in turn preventing them from being raised''.
** Memoria Misera is a very difficult boss. Based on a previous solo instance boss battle against [[spoiler:Emperor Varis (or rather, a highly embellished version of him)]], much of the difficulty from the fight comes from mechanics that require precise synchronized placement of all party members to avoid stacking damage. As the fight moves into its second and third phases, a pair of DPS checks come into play as well, the first requiring both tanks to interacte with designated spots on the map to catch a massive sword beam and succeeding in the ensuing [[ActionCommand Active Time Maneuver]] to survive (emphasis on ''both'' tanks: if one of them is out of play, the other will quickly die and the party will wipe) while the party takes continuous damage, making it a taxing healer check as well. The second DPS check is accompanied by two attacks, one that requires the players to stack to mitigate damage and another that requires the players to spread out to avoid getting hit repeatedly. Each new phase also forces players to contend with more simultaneous mechanics going off. Any mistakes made in dealing with these mechanics can result in a TotalPartyKill. Thankfully, the rewards for winning the fight are well worth it, consisting of high-end armor with five materia slots per piece.
** The Bozjan Southern Front contains three [[DuelBoss Duel Bosses]] ([[MiniMecha Gabriel]], [[TheBeastmaster Beast King Lyon]], and [[PlayingWithFire Sartauvoir the Inferno]]) that can only be fought by finishing an associated Critical Engagement without getting hit and getting selected for the duel in a roulette. Each one requires careful planning of Lost Actions to have any hope of success, and beating all three gives you the achievement title "Sword of the South."
* ''[[Website/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. An 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/GuildWars'' features a few of them, most notably Urgoz, Kannaxi, Mallyx, Duncan the Black, and 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.
* ''VideoGame/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 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]] [[Series/{{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.
* ''VideoGame/RuneScape'' has two types of bosses in its lore: the first are known as quest bosses -- one time fights to advance plot; the other are bonus monsters, where killing them is either a fun way of passing the time, or provides high level loot not available anywhere else. Many of them require quests to access, such as the [[TheUndead Corporeal Beast]]; while others are just in a dangerous area, such as the [[EldritchAbomination Chaos Elemental]]. The FinalBoss title is granted to anyone strong enough to beat 5000 of these bonus bosses, which includes 100 kills of each kind of boss. The Dominion Tower gives rewards for those who can defeat the quest bosses once more.
* There are several in ''VideoGame/StarWarsTheOldRepublic'':
** Commander Mokan in the Battle of Rishi flashpoint on Hard Mode is a very intense coordination and healing check. He has two types of compounds, compound seventeen and compound nine. The group needs to have a balance of both compounds in order to survive. If the player gets 5 stacks of compound nine, they will die instantly. The boss will deliver lots of stacks of this compound to the tank and the healers can only cleanse one stack unless the tank uses injectors of compound seventeen to reduce the number of stacks. Mokan will release compound seventeen to the group so they need to take compound 9 to reduce the damage. It's no surprise that most groups skip this boss.
** 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 Villainy 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.
* ''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.
** 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 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.
** Later 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 a 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!
** The ''Legion'' expansion added what had to be the most GuideDangIt case of this yet, in the form of Endgineer Omegaplugg. To fight him, you have to take a max-level group into the low-level dungeon of Gnomeregan, work your way to the normal final boss of that place, and then find and press a hidden button in that room to summon him. Omegaplugg has many [=AOE=] abilities that can two-shot endgame-geared characters, making the fight extremely difficult on top of all that.
** [[VillainOfAnotherStory The Cow King]] showed up in an event to commemorate ''VideoGame/{{Diablo}}'''s 20th birthday. Getting to him, required killing a sneaky-looking goblin who appeared in some of the raids, which opened a portal to Cow Level in Darkshire.
[[/folder]]

[[folder:Platform Games]]
* ''VideoGame/DukeNukemManhattanProject'' has an immobile green sphere called Wozma as its Bonus Boss. It has about ten times as much health as any other boss in the game and throws explosive barrels at you. Fortunately, you get unlimited ammo for the fight. Unfortunately, its large amount of health makes it a MarathonBoss, taking around half an hour to beat. To get to it you need to press the up arrow at a very specific location shortly before the final boss, which will only show the icon to indicate it's available if you have previously finished the game on Hard, found all the nukes on Hard, and found them all on this play-through, again, on Hard. Beating it just gets you an icon on your saved game. BraggingRightsReward, indeed.
* ''VideoGame/DynamiteHeaddy'' has a Bonus Boss called "The Money" that is unlockable with a password you get by beating the bonus game four times.
* ''Franchise/{{Kirby}}'':
** ''VideoGame/KirbySuperStar'' ''[[VideoGameRemake Ultra]]'' began the tradition of including one at the end of the [[BossRush True Arena]]. This game features [[spoiler: [[BackFromTheDead Marx Soul]]]],who is infamous for his [[SensoryAbuse death screech]].
** ''VideoGame/KirbysReturnToDreamLand'':
*** The game has a Bonus Boss 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:It's the giant Dedede robot seen in the trailer for the cancelled Gamecube ''Kirby'' title that would eventually be retooled into ''Return to Dream Land'', given a new Metal General-themed coat of paint and named "HR-D3".]]
** ''VideoGame/KirbyTripleDeluxe'', has [[spoiler:Shadow Dedede and [[VideoGame/KirbyAndTheAmazingMirror Dark Meta Knight]]]] at the end of [[spoiler:Dededetour!]], as well as [[spoiler:[[TrueFinalBoss Soul of Sectonia]]]] in the True Arena.
** ''VideoGame/KirbyPlanetRobobot'' has the last bosses of [[spoiler:Meta Knightmare Returns: Dark Matter Clone, Sectonia Clone, and Galacta Knight]]. In addition, The True Arena has [[spoiler:[[TrueFinalBoss Star Dream Soul OS]], which has a fourth phase (similar to [[VideoGame/KirbySuperStar Galactic Nova Nucleus]])]] exclusive to it.
** ''VideoGame/KirbyStarAllies'' features [[spoiler:Morpho Knight]] at the very end of the unlockable Guest Star mode after the main story. [[spoiler:He gains a [[ThatOneBoss much]] [[NintendoHard harder]] EX form in the [[HeelFaceTurn Mage Sisters']] Guest Star run, as well as [[BossRush Soul Melter]] [[HarderThanHard EX]]]].
* ''VideoGame/LaMulana'''s infamous [[BrutalBonusLevel 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.
* ''VideoGame/TheLegendaryStarfy'' has Old Man Lobber, who is unlocked by beating all the records in Stage 10. He has BulletHell attacks, and a hard to avoid OneHitKill move when he gets low on health.
* ''VideoGame/TheLegendOfSpyroDawnOfTheDragon'' 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...
* ''Franchise/MegaMan'':
** ''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 UsefulNotes/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/MegaMan9'' has Fake Man, who only appears at the end of a TimeTrial stage bought via DownloadableContent.
*** ''VideoGame/MegaMan10'' features the return of the [[QuirkyMinibossSquad Mega Man Killers]] (Enker, Punk and Ballade) -- again as [=DLC=] Time Trial stages, but unlike with Fake Man, Mega Man (and only Mega Man) can permanently get their weapons.
*** [[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]].
*** ''VideoGame/MegaManRevengeOfTheFallen'' has two of these: [[VideoGame/MegaMan6 Knight Man]] and Bass, who can also be found in [[SecretLevel Knight Man's stage]] in an area that requires his weapon to access, meaning you have to beat the stage twice for HundredPercentCompletion.
*** ''VideoGame/MegaManSuperFightingRobot'' has five of these, unlocked by beating the game in different ways: Bass (beat the game on Hard mode); VideoGame/ShovelKnight (beat the game with over 1,000 screws in reserve); [[Franchise/{{Castlevania}} Simon Belmont]] (beat the game with no upgrades); [[VideoGame/FinalFantasyI Red Mage]] (beat the game with all the upgrades; and Dr. Light (beat the game on [[HarderThanHard Insane]] mode).
*** The ''VideoGame/MakeAGoodMegaManLevelContest'' has two, accessible after collecting all the Energy Elements. A much more powerful Bright Man can be found behind a wall in the attic, and Zero? Soul, a fusion of Zero? and the Trophy Machine is the last enemy fought in [[BossRush The Arena]].
*** The second ''[=MaGMML=]'' has many more: Fighting Milk after defeating the boss of Tier 9 causes it to transform into Strawberry Milk, which keeps the same basic pattern as the original fight but with different and stronger attacks. Birdo, Glass Man, and The Moon from the first game can be fought in Tier 10 after completing the Wily stages, with new patterns and more health. Collecting all 220 Noble Nickels allows you to fight a much, ''much'' more powerful Knight Man. The final room of the [[MarathonLevel Pit of Pits]], also accessible after the Wily stages, is Galaxy Man in a FreeFallFight. Finally, each of the [[BossRush Arenas]] has one of their own as well. The regular Arena has Quick Man anda souped-up [[VideoGame/MegaMan3 Gamma]]; the Mega Arena has an army of Volt Men; and the True Arena has [[TrueFinalBoss Absolute Zero]] again, this time with a new fourth form.
** ''VideoGame/MegaManX'':
*** ''[[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.
*** ''[[VideoGame/MegaManX3 X3]]'' has 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. The player will then fight Mosquitus in the final stages instead - defeating it with Zero is the requirement for X to obtain the Z-Saber. There is also Bit and Byte, whom you can 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 will be replaced in the final stage by Press Disposer. If even one of them is left alive, however, then the player will fight Godkarmachine O Inary in the final stages.
*** ''VideoGame/MegaManX6'' has some bonus bosses by going through alternate routes to fight Zero Nightmare, which unlocks Zero, and High Max, which lets you skip straight to the last areas of the game; it's hard to find out [[GuideDangIt how the hell you're supposed to even damage him]]. Going to the secret areas again will let you fight Dynamo, which lets you get large amounts of souls.
*** ''[[VideoGame/MegaManX8 X8]]'' has 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.
*** ''Mega Man X Legacy Collection 1+2'' has one at the very end of X Challenge mode. Clearing Chapter 9-3 on Hard will throw the player into a secret battle against [[spoiler:Ultimate Armor X and Awakened Zero]].
** In ''VideoGame/MegaManZero3'', 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]].
** 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 Vent/Aile have a much different moveset from [[spoiler:Zero]]. [[spoiler:Omega Zero]]'s AI has also become much more aggressive since the last game, and can defeat you in 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 essentially a powered-up version of Model ZX. Lastly, 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.
** In ''VideoGame/MegaManNetworkTransmission'', if players can obtain every Navi chip in the game, one of which can only be obtained on the "true" ending route, they'll be greeted by an e-mail by Mayl about a rumor of lost area in Den Area 3, which unlocks after beating the game after meeting these conditions. This hidden area will take players to a secret boss battle with [[spoiler:Bass.EXE]].
* ''VideoGame/RatchetAndClank'':
** ''VideoGame/RatchetAndClankFutureACrackInTime'' has [[spoiler:Vorselon, Ratchet's father.....'s accountant.]]
** In ''VideoGame/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.
** Both the [[VideoGame/RatchetAndClankGoingCommando second]] and [[VideoGame/RatchetAndClankUpYourArsenal third]] game of the original trilogy have these in [[MonsterArena Gladiator Arena Challenges]]. The second has four: the first arena includes Chainblade and B2-Brawler -- the latter is pretty difficult to beat when you first enter Maktar Resort. The second arena has Arachnoid and Megapede. The third game has only one dual-bonus boss, Terrible Two -- the second boss, Scorpio, has to be fought later in the game. These bosses appear as separate challenges, challenges with some kind of limitation ([[NoDamageRun taking no damage]], weapons switching on its own ...) and usually take part in some ultimate challenge consisting of many rounds.
* ''VideoGame/TheSimpsonsBartVsTheWorld'': If you collect all the Krusty items, you get to fight Itch and Scratchy.
* ''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.]]
* ''Franchise/SuperMarioBros'':
** ''VideoGame/WarioLandSuperMarioLand3'' has Hinyari, located in [[SlippySlideyIceWorld Sherbet Land.]] Amusingly, you can just walk right out of the battlefield through a convienently-placed door.
** In the fangame ''VideoGame/SuperMarioWorldPiranhaIsland'', there's a secret boss hidden in Darkness Piranha. [[spoiler: It is a recreation of the Master Hand battle from ''Super Smash Bros.'' in the ''Super Mario World'' engine.]]
** In the fangame ''VideoGame/MarioGivesUp'', returning to "Area of Bonuses" after pressing all four switches allows you to reach [[spoiler:the Key Boss]].
[[/folder]]

[[folder:Puzzle Games]]
* The Archivist in ''[[VideoGame/DeadlyRoomsOfDeath 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).
* ''VideoGame/DrMario 64'' has two with similar conditions; if you get through Story Mode on Normal difficulty or higher without losing or restarting a match, then upon defeating Rudy, whichever character you're not playing as will challenge you one last time for the rights to the Megavitamin bottle. If you're playing as Mario, then Wario will power up into [[VideoGame/WarioLand3 Vampire Wario]]; conversely, Wario will have to contend with [[VideoGame/SuperMario64 Metal Mario]]. Defeating them first try will unlock them in Versus Mode, where they're not only [[DefeatMeansPlayable playable]] but also have [[HarderThanHard the hardest AI]].
* ''VideoGame/ProfessorLayton'':
** In ''[[VideoGame/ProfessorLaytonAndTheUnwoundFuture 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 games in the series have each 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.
* Collecting all 24 tickets in ''VideoGame/PonyIsland'' [[spoiler:changes the ending to [[BigGood Hopeless Soul]] telling you that he now understands that you want a satisfying reward for getting full completion and fighting you in a [[SequentialBoss three-stage]] boss battle using different gameplay segments to supply that reward]].
* ''VideoGame/PuyoPuyo'': [[SeriesMascot Carbuncle]] has played this role twice in the series. To wit:
** In ''VideoGame/PuyoPuyoSun'', he can be fought in Schezo's story without using a continue.
** In the first ''VideoGame/PuyoPuyoFever'', he can be fought either by reaching Accord on the Hara Hara route without continuing (while ensuring that Fever mode is used either less than four times or more than twelve) and defeating her or by continuing with a multiple of 7 when defeating her.
* ''VideoGame/PuzzleQuest 2'' has five of them: Kurak the polar bear, the Yeti, the Cave Ogre, the Arch Lich, and the Green Dragon. They're unlocked automatically as you level up, so you can tackle them at your leisure or not at all. Since the rewards they yield aren't any better than most high-end enemies in the game, they aren't worth the effort to beat, unless you're a [[OneHundredPercentCompletion completionist]], an achievement hunter (which you don't even get, depending on the platform) or for the [[BraggingRightsReward bragging rights.]]
* ''VideoGame/SutteHakkun'' has the Purple Makkun, an [[UniformityException odd-colored]] Makkun that hides within specific crevices in certain stages in every world, serving as the replacement for the [[BonusStage Bonus Stages]] of the Satellaview versions. He's the only character in the entire game that attacks you in any form: upon finding him, he'll scoop you up and challege you to [[RacingMinigame a race]] in one of his ten Battle stages (which have the same level of [[NintendoHard difficulty]] as the regular stages). Beat him, and you'll [[spoiler:get a segment of the Solution code to write down.]]
[[/folder]]

[[folder:Racing Games]]
* In any version of ''VideoGame/InitialDArcadeStage'', defeating all opponents in Legend Of The Streets mode ''once per loop'' will take you to a free battle with the game's TrueFinalBoss, Bunta Fujiwara. He is extremely difficult to beat, often sporting RubberBandAI. Whether or not you defeat him, the credits will roll afterwards.
* ''VideoGame/MarioKartDS'' has Giant Wiggler, the boss of the secret set of Mission Mode levels that is unlocked after earning at least one star in each of the regular missions. Due to its size, it runs incredibly fast, so you have to use the Star at all times to win the race (luckily, all Item Boxes have Stars and nothing else).
* ''Speed Freaks'' (also known as ''Speed Punks''), a relatively obscure ''Mario Kart''-style Racer for the [=PS1=], had three Bonus Bosses. If you place first in every race in one of the game's three tournaments, the game immediately takes you to a one-on-one, no-powerups race against a SecretCharacter, and if you win, you [[DefeatMeansPlayable unlock them as playable]]. However, winning these races isn't necessary to complete the game, and [[AntiFrustrationFeatures mercifully you don't have to win each tournament again to have another shot if you lose.]] Note that the first two, [[CanineCompanion Cosworth]] and [[TokenMinority Tetsuo]], [[DefiedTrope defy]] the usual Bonus Boss difficulty expectations by actually being slightly ''[[BossDissonance easier]]'' than the NintendoHard [[HardLevelsEasyBosses regular races]]. On the other hand, the third and final Bonus Boss, [[RobotBuddy Beemer]], is [[ThatOneBoss controller-snappingly difficult]], even compared to the rest of the game, and is a worthy candidate for the hardest Boss in a Racing Game ''ever''. This is due to a combination of insane [[RubberBandAI Rubber-Banding]], PerfectPlayAI, and the fact that you're racing him on [[ThatOneLevel That One Track]]; an [[MarathonLevel inconceivably long]] series of tricky, twisty turns and awkward, hard-to-find shortcuts which the AI not only uses, but can pull off perfectly every single time. All this means that he's likely to get an eternity's lead on you in the first few seconds of the race, and the margin for error is non-existent. Even if you drive flawlessly and maintain a solid lead for the majority of the race, a single mistake at any time will have him zooming past you, never to be seen again. All this means you'll have blisters on your thumbs by the time you finally beat him, if you manage that without [[RageQuit Rage-Quitting]].
[[/folder]]

[[folder:Real-Time Strategy]]
* ''[[VideoGame/DawnOfWar Dawn of War 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.
* The enemy fountain from ''VideoGame/DefenseOfTheAncients''. It will fuck up anyone who goes in unprepared, and [[InstantWinCondition its destruction is completely unnecessary]].
* ''VideoGame/DefenseOfTheAncientsAllStars'' and its sequel ''VideoGame/Dota2'' has Roshan, extremely hard to defeat single-handedly, but defeating it will yield a good boon to the team that defeated it.
* ''VideoGame/HeroesOfTheStorm'' has either golem-like mercs or various others, depending on the map.
* ''VideoGame/LeagueOfLegends'' has Baron Nashor (and Vilemaw for Twisted Treeline map).
* ''VideoGame/{{Mindustry}}'' has an interesting variation of this trope -- ''all'' bosses spawn much later than what you need to do to achieve the victory condition on their respective maps, and in early game you likely won't even encounter them unless you were deliberately aiming for HardModeFiller.
* From the Creator/ParadoxInteractive strategy games:
** ''VideoGame/CrusaderKings'': With the ''Jade Dragon'' [=DLC=], ImperialChina is added as an offscreen empire that rulers can negotiate with. If you meet certain strict requirements (you must be an Empire-tier ruler with 300 counties in your realm, you must border the eastern edge of the map and China must not be destabilized) you can invade China. The war itself is extremely hard, as China sends huge armies larger than even the Aztecs while your own armies suffer -75% replenishment, and losing [[BalkanizeMe means your empire is shattered into pieces]] so you can never threaten the middle kingdom again, but if you win you install a family member in the Chinese dynasty and gain huge spoils of war.
** ''VideoGame/HeartsOfIron'': You can use a console command to spawn an AlienInvasion on a province of your choice[[note]]Alienattack[province number], so "alienattack772" results in the aliens attacking Roswell, USA[[/note]]. The aliens [[NothingIsScarier have no ministers]] and very powerful free troops with the latest technologies. Outside of this cheating, the Soviet Union is likely to eventually become this if you are playing as one of the western Allies and the war against the Axis concludes (and vice versa), and if the Axis defeat the Allies before the USA joins then they will probably end up being your dessert in the same way.
** ''VideoGame/{{Stellaris}}'': Fallen Empires. You don't actually have to fight them (unless you're playing as [[AbsoluteXenophobe Fanatic Purifiers]] or [[spoiler:[[AwakeningTheSleepingGiant they wake up]]]]) but the huge resource output of their planets, access to rare Strategic Resources and their incredible technology will surely make you a galactic superpower if you can overthrow them. There's also the Leviathans added in the [=DLC=] pack of the same name, which are powerful single entities that stay in a home system but give you a boon if you can beat them.
* ''VideoGame/{{Pikmin}}'':
** ''VideoGame/Pikmin1'': You have to go out of your way to find the fight the Smoky Progg (and do so before the end of Day 15, [[PermanentlyMissableContent or else it'll disappear forever]]) 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.
** ''VideoGame/Pikmin3Deluxe'' features a new boss at the end of the "Olimar's Comeback" sidestory: [[spoiler: a golden mix between a Shaggy Long Legs and the otherwise-absent Raging Long Legs from ''Pikmin 2'']]. Since it's not part of the main game, it lacks a Piklopedia entry and thus goes unnamed.
%%* ''VideoGame/{{Smite}}'' has the Fire Giant (and [[Myth/EgyptianMythology Apophis]] for the Clash map).
[[/folder]]

[[folder:Rhythm Games]]
* ''VideoGame/{{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]]). ''VideoGame/BeatmaniaIIDX'' 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.
* In ''VideoGame/BustAGroove 2'', getting "Fever Time" in each level lets you face off against Pander, a [[NonstandardCharacterDesign photorealistic middle-aged bald man wearing nothing but briefs, a single shoe, and body paint vaguely resembling a panda]] whose dance style is inspired by traditional Japanese [[https://en.wikipedia.org/wiki/Butoh Butoh]] and whose stage is a WhiteVoidRoom with screens displaying seemlingly random black-and-white photographs before turning into an AmazingTechnicolorBattlefield. Unlike every other character, he doesn't have one specific set of combos, meaning that his fight will be unique almost every time. Beating Pander as Robo-Z Gold, the game's standard FinalBoss, lets you play as him.
* From ''VideoGame/{{DJMAX}}'' Technika:
** In the Specialist set, getting 70% accuracy or lower nets you [[https://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 [[https://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 [[https://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 [[https://www.youtube.com/watch?v=A_QVFGjiWvg D2]], a song running at 356 BPM (approximately 1.5 times faster than Son of Sun); and to unlock this song, you'll have to play a very, very buggy song called [[https://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.
* ''VideoGame/{{Everhood}} has the Spirit of Light, who, when beaten, gives you one of the three gems needed for one of the MultipleEndings.
* ''VideoGame/FredericResurrectionOfMusic'' has three optional songs/opponents that can be fought in Arena Mode. You need to beat the game three times (once for each difficulty except Too Easy) to unlock them all.
* ''VideoGame/GuitarHero'':
** [[https://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: "[[https://www.youtube.com/watch?v=H8Xb5XyY5cE Jordan]]" from ''VideoGame/GuitarHero II''. The note chart for this song isn't as horrible, but since Guitar Hero II gives much less time for you to hit each note, the difficulty is comparable.
** ''Satch Boogie'' for Guitar Hero World Tour.
** The spiritual successor "Visions" from ''Rock Band 2'', utterly punishing on both [[https://www.youtube.com/watch?v=DJralxgefcE guitar]] and [[https://www.youtube.com/watch?v=RoHWwrTeYLY drums]].
* ''VideoGame/{{maimai}}'' has the Challenge Track system, in which you get to play a new song with a limited number of lives. Getting anything below a Perfect will take lives away. The newer the challenge, the less lives you have; if you go for it on the first day it's available, you have only one life (i.e. get an All Perfect or else you fail).
[[/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/TheBindingOfIsaac'': ''Afterbirth'', the DLC for the remake ''Rebirth'', provides one in the form of [[spoiler:Hush]]. Beating it the first time will end your run, but the fight itself is optional and subsequent fights will allow you to progress to the next floor after you defeat it. Averted in the next expansion, ''Afterbirth+'', where it has to be fought to unlock the TrueFinalBoss, [[spoiler:Delirium]]. The scoring system encourages fighting [[spoiler:Hush]] for getting a high score in daily runs, as it and the BossRush each give out thousands of points on completion.
* ''VideoGame/DarkestDungeon'' has the Shambler, which can normally only be fought be activating a certain foreboding-looking altar with writing on it clearly stating that it's [[SchmuckBait a very bad idea]]. The monster is not only very strong, but fights in an unorthodox way which is sure to surprise the player in the first fight.
* ''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 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 the quickest possible suicide you can find in a game with plenty of them.
* In ''VideoGame/EnterTheGungeon'', if you spend a total of 1000 coins on a certain item and use it to access a hidden floor beneath the Black Powder Mines, you'll end up running into [[spoiler:the Resourceful Rat, who's likely stolen a ton of goods that you left behind]]. This is a long, difficult fight that consists of multiple phases (the High Dragun and [[spoiler:the Lich]] are the only other bosses with this distinction), with the third and final phase [[UnexpectedGameplayChange playing absolutely nothing like the rest of the game]]. If you win, though, you're treated to a stash of items, weapons and pick-ups.
* In ''VideoGame/FTLFasterThanLight'', within the Rebel Stronghold sector, there is a huge shipyard. If decide to explore it, you find an unfinished second rebel flagship. [[FinalBossPreview It is the 3rd phase]] of the hard mode [[FinalBoss Rebel Flagship]], but its systems are weaker, it has less crew, no mind control, [[spoiler: [[DesperationAttack no power]] [[BeamSpam surge]], and no AI takeover on crew death.]] Defeating it delays the [[AdvancingWallOfDoom Rebel Fleet]], grants you a very large reward, and unlocks the Federation Cruiser.
* ''VideoGame/{{Hades}}'': During any run, it's possible to initiate a fight with [[spoiler:Charon]] by [[spoiler:[[ShopliftAndDie "borrowing" obols from his shop]]]]. While he's not very fast, he has a monstrous amount of health, spams a small arena with a constant barrage of attacks, and does the most damage in a single hit of any boss in the game, including the FinalBoss. However, if Zagreus beats him [[spoiler:he'll get to keep the "borrowed" money and will even be given a membership card that cuts 20% off all future shop purchases for that run.]]
* ''VideoGame/NetHack'' has Demogorgon, a demon prince that can only be randomly summoned by other major demons. He has devastating attacks, so the best strategy against him may be to never meet him at all. However, a wielded cockatrice corpse can [[TakenForGranite instantly petrify him]]. There are other demon princes that need to be summoned in order to appear, like Geryon, but Demogorgon is by far the most feared of them.
* ''VideoGame/SlashEmExtended'', a variant of ''VideoGame/NetHack'' variant ''VideoGame/SlashEM'', has even more. Pale Night, Verier, Baalphegor and many other demon lords and princes can be summoned by major demons but don't appear randomly.
[[/folder]]

[[folder:Shoot 'em Ups]]
* ''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.
* ''VideoGame/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 six normal bosses of ''[[VideoGame/DonPachi DoDonPachi]]'' (Suzaku, Senkou, Kakou, Raikou, Rankou and Ryuukou) as bonus mid-bosses, triggered by fulfilling certain conditions.
* The giant space worm of ''VideoGame/EventHorizon'', which can be [[RandomEncounter randomly encountered]] in Beacon events. It sends out a [[HordeOfAlienLocusts Horde Of Alien Locusts]] at the player in addition to normal attacks, and [[SubsystemDamage you have to destroy its tail segments]] before you can deal any meaningful damage to it. [[spoiler: The same enemy appears later on as the boss of one of endgame factions.]]
* ''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.
* ''VideoGame/{{Hellsinker}}'', as with [[VideoGame/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, [[https://www.youtube.com/watch?v=X00wKV3SYIE you're in for a world of hurt]].
* 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.
* In the [=PS2=] remake of ''VideoGame/SpaceHarrier'', continuing to fire at the end of Stage 19 results in the game continuing for four more stages, with twin fire dragons Haya-Oh awaiting at the end of #22.
* Always present in ''Franchise/TouhouProject'' games ever since ''Story of Eastern Wonderland''. Typically, after beating the FinalBoss, the heroines once again investigates another, smaller incident in the [[BonusDungeon Extra Stage]] that is caused by the Bonus Boss.
** In ''VideoGame/TouhouFuumarokuTheStoryOfEasternWonderland'', the stage 1 boss Rika returns with her newest tank creation, the Evil Eye Sigma.
** In ''VideoGame/TouhouGensokyoLotusLandStory'', the heroine [[ExcusePlot just kind of wanders into another dimension]] and fights its creator, Mugetsu. After you beat her, Mugetsu's older sister Gengetsu comes in and fight you instead. Unlike other extra bosses, they have absolutely no relations to the main plot and even the heroines are wondering why they're there in the first place.
** In ''VideoGame/TouhouKaikidanMysticSquare'', the stage 3 boss, Alice, returns for a revenge match using powerful magic from her undealed grimoire.
** In ''VideoGame/TouhouKoumakyouTheEmbodimentOfScarletDevil'', after storming the Scarlet Devil Mansion to beat [[FinalBoss Remilia Scarlet]], her [[StrongerSibling younger sister Flandre Scarlet]] is kicking up a fuss and you need to return there and stop her.
** ''VideoGame/TouhouYouyoumuPerfectCherryBlossom'' had an ''extra'' Extra Stage with an ''extra'' Extra Boss. You're looking for Yukari Yakumo so she can fix the broken border between Gensokyo and the Netherworld. In the first extra stage she's not available, so you face off against her subordinate Ran Yakumo, instead. In the second extra stage (called Phantasm Stage) you face off against Yukari proper.
** ''VideoGame/TouhouEiyashouImperishableNight'', [[FinalBoss Kaguya]] sends you on a test of courage, but it's actually her sending you as assassins against her longtime rival and fellow immortal Fujiwara no Mokou. You fight Mokou just because.
** In ''VideoGame/TouhouFuujinrokuMountainOfFaith'', you hear about the second god of the Moriya Shrine, so you return there and meet Suwako Moriya, who promptly challenges you for a danmaku battle for fun.
** [[LampshadeHanging Lampshaded]] in the 11th game, ''VideoGame/TouhouChireidenSubterraneanAnimism''. 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." The page quote is the start of that conversation. Story-wise, you heard that the ones empowering [[FinalBoss Utsuho]] are the gods of the Moriya Shrine, so you return there once again. They're not present, but instead you meet Koishi Komeiji, who is also looking for them for the power.
** In ''VideoGame/TouhouSeirensenUndefinedFantasticObject'', you discover that [[FinalBoss Byakuren's]] crew are completely clueless about the [=UFOs=] floating around, so this time you go and meet the real culprit, Nue Houjuu.
** In ''VideoGame/YouseiDaisensouTouhouSangetsusei'', Cirno, who's drunk with power after defeating the Three Fairies, started picking fights to prove she's the strongest. Marisa Kirisame decided to humor her and took up the challenge.
** In ''VideoGame/TouhouShinreibyouTenDesires'', Mamizou Futatsuiwa is supposed to be a reinforcement against [[FinalBoss Miko]], but you've already beaten her. Mamizou then challenges you for a fight, anyway.
** In ''VideoGame/TouhouKishinjouDoubleDealingCharacter'', most [[AnimateInanimateObject tsukumogami]] spawned from the Miracle Mallet has reverted to being normal objects. Except for Raiko Horikawa, who has found a way to keep her sentience without relying on the mallet. She then tries to test her newfound power on you.
** In ''VideoGame/TouhouKanjudenLegacyOfLunaticKingdom'', you've beaten Junko and supposedly freed the Lunarians. However, the Lunarians are still being kept captive in the Dream World by Junko's ally, hell goddess Hecatia Lapislazuli.
** ''VideoGame/TouhouTenkuushouHiddenStarInFourSeasons'' shakes things up a bit. Canonically, you lost against the FinalBoss Okina Matara in the normal story mode. In the Extra Stage (called Revenging Stage in the game), you return for a rematch against her and end the incident proper. This is the first time the FinalBoss and Bonus Boss are the same character in ''Touhou''.
** In ''VideoGame/TouhouKikeijuuWilyBeastAndWeakestCreature'', Saki Kurokoma, one of the leaders of the Animal Realm, took advantage of the power vacuum created after you beat [[FinalBoss Keiki]] and launched an invasion to neighboring realms. It's up to you to stop her.
** In ''VideoGame/TouhouKouryuudouUnconnectedMarketeers'' Chimata has been beaten, but the Rainbow Dragon Cave has not been fully explored due to its lack of oxygen, and Megumu has sent out Tsukasa to fight with Misumaru upon learning about their existence and deeming them a mine looter. Using a special Ability Card that grants them the ability to breathe in anoxic enviroments, the protagonists brave the Rainbow Dragon Cave once again and face Momoyo Himemushi, an ''oomukude'' and supplier of dragon gems for Megumu, making the whole Ability Card scheme possible in the first place.
* ''VideoGame/{{Tyrian}}'' has the 'Revenge of Zinglon' bonus game that you can access if you beat the main game with a certain route. The multi-stage boss there isn't all that much tougher than many of the other bosses in the game, but what makes it ridiculously hard is that all your ship's weapons and powerups are removed and you are stuck with a basic railgun that takes a long time to upgrade, and to top it all off, you can't use cheats.
[[/folder]]

[[folder:Simulation Games]]
* Lots of missions in the ''VideoGame/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 ''VideoGame/AceCombatZeroTheBelkanWar'': [[spoiler:Mobius One and his Raptor]] are encountered in an Ace difficulty run of [[BossRush The Gauntlet]] if you do well enough. Similarly are [[spoiler: Scarface One and ZOE Commander]] in a certain mission in ''VideoGame/AceCombatXSkiesOfDeception''.
* 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 ''VideoGame/RocketKnightAdventures'' series count, too.
* 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.
[[/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 Creator/{{Konami}}'s ''NFL Football'' for the UsefulNotes/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]], souped up versions of the military vehicles and AI weapons, ''[[NintendoHard custom]]'' versions of these bosses, and all of the [[spoiler:Monster Hunter]] bosses.
[[/folder]]

[[folder:Survival Horror]]
* ''VideoGame/FatalFrame1'' 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.
* ''VideoGame/FiveNightsAtFreddys4'' has ''Nightmare Mode,'' which involves you facing off against a scarier, smarter, and all around more intense Fredbear aptly named "Nightmare".
[[/folder]]

[[folder:Third-Person Shooter]]
* ''VideoGame/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.
* ''VideoGame/Splatoon2'''s ''Octo Expansion'' has [[spoiler:Inner Agent 3]], accessible after collecting all of the Mem Cakes. Appropriately, the framing device is [[spoiler:Agent 8 reliving their memory of fighting [[PreviousPlayerCharacterCameo Agent 3]] in [[VideoGame/{{Splatoon}} the first game]]]]. It's a [[SNKBoss fairly difficult]] five-phase fight with CheckpointStarvation, with the boss throwing Auto Bombs often, having short cooldowns on their specials, and performing other techniques that wouldn't be possible in normal gameplay. Defeating them unlocks the [[AndYourRewardIsClothes Golden Toothpick]] headgear for multiplayer battles.
[[/folder]]

[[folder:Turn-Based Strategy]]
* ''VideoGame/FinalFantasyTactics'' gave us Elidibs and the Zodiac summon.
* In the ''Franchise/FireEmblem'' franchise:
** In ''VideoGame/FireEmblemGenealogyOfTheHolyWar'', 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.
** ''VideoGame/FireEmblemPathOfRadiance'' has General Bryce of Daein. 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. If you take him on and take him out, you can loot the most powerful lance in the game, [[InfinityPlusOneSword the Wishblade]]. It is, however, entirely possible to avoid fighting Bryce by taking another route.
** ''VideoGame/FireEmblemRadiantDawn'' has Levail, General Zelgius's apprentice and Bryce's successor as the wielder of the Wishblade. 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 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 the Wishblade.
** 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[[labelnote:For Reference...]]Not including the Streetpass Characters, Awakening has a total of ''48'' recruitable units (not including Priam). In other words, this battle allows you to take more than ''62%'' of your ''entire army''.[[/labelnote]]. [[spoiler:Priam]] himself is equipped with three Breaker skills, Sol, Luna, and nearly maxed stats making him quite a challenge to defeat.
** ''Fire Emblem Echoes: Shadows of Valentia'', the [=3DS=] remake of ''VideoGame/FireEmblemGaiden'', has the Creation, a monster encountered at the bottom of the Thabes Labyrinth which can be accessed after the game is completed. It's heavily implied that the Creation is actually [[spoiler:a young version of Grima, the main antagonist of ''Awakening'']].
* ''VideoGame/LuminousArc2'' has the reoccurring boss for the optional ThatOneSidequest Spa Battle series, [[spoiler:[[VideoGame/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.
* Creator/NipponIchi games:
** Demon Supreme Overlord Baal in the ''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 level 9999. 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}}''. 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 Bonus Boss, 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 a requirement to raise the stationary attack bonus as high as possible to take him down and even then he's still a MarathonBoss.
** Tyrant Overlord Baal in D2 goes above and beyond the call of duty as a boss. It's not just the boss fight itself that's a marathon. It's preparing for the fight that is an Iron Triathalon itself. Getting the levels and stats of your characters, weapons, and gear high enough to fight him and have a chance at winning can take dozens upon dozens upon dozens of hours of gameplay. Strap yourself in, tighten up that sphincter, and notify your loved ones that you might be unavailable for a while, as you can end up dedicating days or even weeks on end to just preparing for this boss fight.
* Fera in ''VideoGame/TelepathTactics'', an extremely high-level swordfighter wielding an InfinityPlusOneSword. You fight her at the end of the first arc, which is a point where she can probably one-shot anyone on your team. Similarly to General D'Kah in [[VideoGame/TelepathRPGServantsOfGod the previous game]], you are expected to run from her, but it is possible to beat her, either by prior LevelGrinding or by abusing [[SuperDrowningSkills terrain damage]].
* In the postgame of ''VideoGame/YuGiOhMonsterCapsuleGB'', you can duel Joey, Tea, Tristan, Ryou, Grandpa, Pegasus, Bandit Keith, Shadi, Yami Bakura, and a freed Seto Kaiba. The latter two have the toughest monsters in the game.
[[/folder]]

[[folder:Visual Novel]]
* ''VisualNovel/LuxPain'' zigzags between this and SkippableBoss. Most bosses have to be fought as part of the game, but some can only be encountered by following the right events (or even sequences of events) that only become available at certain points and lock again afterwards (hence the zigzag - there is no 'default' way through most of these sections, so whether you encounter them or not is just down to where you looked when you had the chance). This includes battles with the SILENT in the minds of Honoka, Sakai and even Mint the ghost cat.
[[/folder]]

[[folder:Wide Open Sandbox]]
* By the same token, nothing in ''VideoGame/DwarfFortress'' says you ''have'' to find the [[ItWasHisSled Hidden Fun Stuff]]. Or [[OurAngelsAreDifferent the Vaults]], for that matter, if you're an Adventurer instead. Both will give you utter hell even by the game's standards.
* Both bosses in ''VideoGame/{{Minecraft}}'' are optional. The first is the Enderdragon, which doubles as a FinalBoss. 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.
* ''VideoGame/{{Terraria}}'':
** King Slime's main purpose is giving the cosmetic [[AndYourRewardIsClothes Ninja armor]] (he can drop a slime mount and on Expert gives the useful Royal Gel that turns all slimes neutral). He can appear randomly in the outer parts of the map, but killing him is never required to progress through the game.
** Queen Bee unlocks the non-essential Witch Doctor NPC and has good low-level gear, but is otherwise optional.
** Duke Fishron could be about as challenging as the FinalBoss and drops a lot of good stuff, but is [[GuideDangIt comparatively hard to summon]] and doesn't advance the world at all.
** The Empress of Light is an optional BulletHell boss with tougher stats than even Duke Fishron, but good drops. She has a special drop that can only be obtained if all damage to her is done during the day, during which all of her attacks kill the player with one hit.
** The optional Pumpkin and Frost Moons both have at least two bosses that have a higher chance of dropping good weapons the more waves the player fights through. Their most dangerous bosses are the Pumpking and the Ice Queen, respectively, which by themselves already have stats on par with the regular Hardmode bosses, but later waves have the payer fighting multiples of them at once.
** The Old One's Army is an optional crossover event themed on tower defense. Its third and most difficult tier ends with with fighting Betsy, a giant fire-breathing dragon who could prove to be difficult to take on even with endgame-tier equipment. She must be fought while ''also'' dealing with the enemies from previous waves.
[[/folder]]

!!Non-Video Game Examples

[[folder:Fan Works]]

* ''Fanfic/MariaCampbellOfTheAstralClocktower'': In-universe, PlayedForLaughs. In this fic, once Creator/HidetakaMiyazaki finished the ''VideoGame/DarkSouls'' series, he decided to make... an otome game. For some reason. ''Fortune Lover'' was therefore an absolutely bizarre game with all of Miyazaki's signature touches, including optional bosses of infamous difficulty. Katarina constantly complains about how she used to die all the time in the game, and is very sympathetic towards Maria for accidentally getting into these boss battles (though thankfully she's much tougher than in the game).
-->'''Katarina:''' Why are there bosses in an otome game!? You don't even have weapons!

[[/folder]]

----

*** ''Mega Man X Legacy Collection 1+2'' has one at the very tail end of X Challenge mode. Clearing Chapter 9-3 on Hard will throw the player into a secret battle against [[spoiler:Ultimate Armor X and Awakened Zero]].

** To fight the Smoky Progg in the first game, have to go out of your way to find it (and do so before the end of Day 15, [[PermanentlyMissableContent or else it'll disappear forever]]) 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.
** ''VideoGame/Pikmin3 [[UpdatedRerelease Deluxe]]'' features a new boss at the end of the "Olimar's Comeback" sidestory: [[spoiler: a golden mix between a Shaggy Long Legs and the otherwise-absent Raging Long Legs from ''Pikmin 2'']]. Since it's not part of the main game, it lacks a Piklopedia entry and thus goes unnamed.
* ''VideoGame/{{Smite}}'' has the Fire Giant (and [[Myth/EgyptianMythology Apophis]] for the Clash map).

** The fifth Headhunter DLC, ''Sir Hammerlock vs. the Son of Crawmerax'', adds one raid boss in the form of the colossal craboid, The Invincible Son of Crawmerax the Invincible. Crawmerax actually the least health of all the raid bosses in Borderlands 2, sitting at just 11,674,231,808 health on Overpower 10.
The fifth story DLC, ''Commander Lilith & the Fight for Sanctuary'', adds one last raid boss in the form of Haderax the Invincible. Haderax is a giant, purple Sand Worm. He has a staggering 78,914,863,104 health on Overpower 10.

** 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 Vermivorous The Invincible]].

** ''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.

** 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)"]]'''

** 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 (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''.

** Dexiduous the Invincible, A '''''secret''''' secret boss from the same DLC, a colossal [[BigCreepyCrawlies drifter]], is the single largest enemy in the series. It costs over 100 Iridium to summon, and even then, you have to fight trough hordes of Badass and '''''Super Badass''''' enemies before it will even appear. It can only be damaged by hitting it's critical spots, and it has HP in the '''''MILLIONS.'''''

** In ''Sun'', he can be fought in Schezo's story without using a continue.

** In the first ''Fever'', he can be fought either by reaching Accord on the Hara Hara route without continuing (while ensuring that Fever mode is used either less than four times or more than twelve) and defeating her or by continuing with a multiple of 7 when defeating her.

[[folder:Action Adventure Games]]

* BonusBoss/RolePlayingGames
----

* ''VideoGame/{Everhood} has the Spirit of Light, who, when beaten, gives you one of the three gems needed for one of the MultipleEndings.

** ''VideoGame/AssassinsCreedRogue'', being somewhat of a MissionPackSequel to ''Black Flag'', copies the latter's four legendary ship battles, only this time it's against entire fleets led by a souped-up flagship. Thankfully you get an AI fleet of your own as backup, but you'll still be doing most of the heavy lifting. Winning all four battles then unlocks the real superboss, the ''Storm Fortress'', flagship of the Assassin fleet and an insanely powerful Man o' War that's fought amidst a raging thunderstorm. When its health drops to about 30% it summons backup in the form of two additional level 70 Man o' Wars that fight exactly like the [[DualBoss HMS Fearless and Royal Sovereign]] mentioned above.

* The ''Franchise/AssassinsCreed'' franchise introduced bonus bosses starting with ''VideoGame/AssassinsCreedIVBlackFlag''.

** ''VideoGame/AssassinsCreedOdyssey'' has a huge number of bonus bosses drawn from Ancient Greek mythology, ranging from eight legendary animals to cyclopses, the Minotaur, the Sphinx, and even a bunch of Greek gods up to and including Hades himself. However, the definition of what counts as a BonusBoss is a bit murky in this installment due to its multiple independent story arcs, many of which are tied to DownloadableContent. For instance, the mythical monsters like the Sphinx are bonus bosses in the main game but mandatory for the DLC arcs that lead to the game's true final ending.

** ''VideoGame/AssassinsCreedRogue'', being somewhat of a MissionPackSequel to ''BlackFlag'', copies the latter's four legendary ship battles, only this time it's against entire fleets led by a souped-up flagship. Thankfully you get an AI fleet of your own as backup, but you'll still be doing most of the heavy lifting. Winning all four battles then unlocks the real superboss, the ''Storm Fortress'', flagship of the Assassin fleet and an insanely powerful Man o' War that's fought amidst a raging thunderstorm. When its health drops to about 30% it summons backup in the form of two additional level 70 Man o' Wars that fight exactly like the [[DualBoss HMS Fearless and Royal Sovereign]] mentioned above.

* In ''VideoGame/AssassinsCreedIVBlackFlag,'' there are five legendary ships that you can fight in any of the four corners of the map: The [[LongRangeFighter HMS Prince]], who will pester you from afar with mortar shots, [[NighInvulnerability La Dama Negra]], who can only be fired at from behind, The [[DualBoss HMS Fearless]] and The [[DualBoss Royal Sovereign]], who will surround and double-team you, and the [[ThatOneBoss infamous]] [[LightningBruiser El Impoluto]], who uses her greater speed and maneuverability to ram your elite hull armor to oblivion. You win 20,000 Reales for winning each fight, but by that point you've probably bought all the ship upgrades you needed to actually beat them, so it's more of a BraggingRightsReward. Defeating all five ships gives the ''Jackdaw'' the ''El Impoluto'''s boosted ram attack, but then again, by that point there's not much left to use it on.

* In ''VideoGame/AssassinsCreedIVBlackFlag,'' there are five legendary ships that you can fight in any of the four corners of the map: The [[LongRangeFighter HMS Prince]], who will pester you from afar with mortar shots, [[NighInvulnerability La Dama Negra]], who can only be fired at from behind, The [[DualBoss HMS Fearless]] and The [[DualBoss Royal Sovereign]], who will surround and double-team you, and the [[ThatOneBoss infamous]] [[LightningBruiser El Impoluto]], who uses her greater speed and maneuverability to ram your elite hull armor to oblivion. You win 20,000 Reales for winning each fight, but by that point you've probably bought all the ship upgrades you needed to actually beat them, so it's more of a BraggingRightsReward.

* ''VideoGame/RuneScape'' has two types of bosses in its lore: the first are known as quest bosses -- one time fights to advance plot; the other are bonus monsters, where killing them is either a fun way of passing the time, or provides high level loot not available anywhere else. Many of them require quests to access, such as the [[{{Undead}} Corporeal Beast]]; while others are just in a dangerous area, such as the [[EldritchAbomination Chaos Elemental]]. The FinalBoss title is granted to anyone strong enough to beat 5000 of these bonus bosses, which includes 100 kills of each kind of boss. The Dominion Tower gives rewards for those who can defeat the quest bosses once more.

* ''VideoGame/HollowKnight'' unlocks a large number of optional bosses once you acquire the Dream Nail, some distinctly more difficult than others. The Warrior Dreams encountered at ceremonial gravesites and fought on the main map talk tough but are relatively easy to defeat, and defeating a few of these for their Essence is practically mandatory to achieve the good ending. The upgraded versions of normal bosses killed ''by the player'' and refought in off-the-map pocket dimensions, however, generally exceed the normal FinalBoss in difficulty.

** ''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.]]

* In the fangame ''VideoGame/MarioGivesUp'', returning to "Area of Bonuses" after pressing all four switches allows you to reach [[spoiler:the Key Boss]].

* In the fangame ''VideoGame/SuperMarioWorldPiranhaIsland'', there's a secret boss hidden in Darkness Piranha. [[spoiler: It is a recreation of the Master Hand battle from ''Super Smash Bros.'' in the ''Super Mario World'' engine.]]