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Bonus Boss
aka: Super Boss

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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, Touhou Chireiden ~ Subterranean Animism, Extra Stage
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The Bonus Boss is a type of Optional Boss 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 Final Boss. Sometimes this is justified with an in-universe explanation, but more often than not, it's a glaring example of Giant Space Flea from Nowhere, which itself is a subtrope of Gameplay and Story Segregation. Another common nickname for them is "Superboss."

There's no real limit to the number of bonus bosses you can fight; Final Fantasy X had dozens of them cordoned off in the optional (and highly incongruous) Monster Arena. The key features are that defeating one isn't necessary to complete the game, and they require quite a bit of conscious effort to find. Their usual habitat is the end of a Bonus Dungeon, Brutal Bonus Level, sidequest, or Boss Rush. If a late-game boss has multiple difficulty levels, expect the absolute highest level to be considered a bonus boss, if not the True Final Boss.

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Like any good Boss Battle (or Final-Exam Boss), when fighting them, it's pretty damn useful to anticipate their actions. It's demanding but strategic. Prizes can include anything from an Infinity +1 Sword or Last Disc Magic to a simple Cosmetic Award. The lure of overcoming an extremely dangerous enemy is enough for 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 for bragging rights. The game then picks up from there and just pretends the bonus boss never happened.

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

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Contrast Skippable Boss, 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 Sequence-Break.

A Legacy Boss is a Bonus Bonus that happens to be a character from a previous installment.

A Bonus Boss that drops useful items may lead to Unstable Equilibrium. Compare Secret Character for hard-to-find Player Characters.


Examples:



    open/close all folders 

    Action Adventure Games 
  • 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, Simon Says, with a very useful third cooking slot as your reward for playing well.
  • In Assassin's Creed IV: Black Flag, there are five legendary ships that you can fight in any of the four corners of the map: The HMS Prince, who will pester you from afar with mortar shots, La Dama Negra, who can only be fired at from behind, The HMS Fearless and The Royal Sovereign, who will surround and double-team you, and the infamous 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 Bragging Rights Reward.
  • Bloodstained: Ritual of the Night: 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 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 Kickstarter Edition of the game gets to challenge an extremely difficult secret boss for a shot at acquiring the Swordwhip.
  • Castlevania series:
    • Castlevania: Order of Ecclesia 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 Castlevania: Symphony of the Night 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 Castlevania: Curse of Darkness.
    • The Whip's Memory, an image of Richter Belmont in Castlevania: Portrait of Ruin, is part of a ritual to unlock the true power of a 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.
    • Castlevania: Lament of Innocence has The Forgotten One, a giant, skinless demon trapped in the Prison of Eternal Torture, an area accessible when you open the Hub Level. (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. Unless you use the Ice Whip.
  • Doctor Lautrec and the Forgotten Knights: 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.
  • Dragon's Dogma 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 Damage-Sponge Boss 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 Death as a repeating boss encounter on Bitterblack Isle. It, too, is a Damage-Sponge Boss 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 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.
  • God of War (PS4) 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.
  • Hollow Knight 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 Final Boss in difficulty.
  • Illusion of Gaia has Solid Arm, a boss originally from the first game in the series, SoulBlazer, who's only fightable if you collect all fifty Red Jewels.
  • Ittle Dew has one at the end of the Master Cave. Oddly, it's the one boss you beat through brute force rather than some kind of puzzle.
  • The Legend of Zelda:
    • The Legend of Zelda: A Link to the Past:
      • The Four Sword Links in the remake on the Game Boy Advance. Each Link had some abilities that Link could use, such as the Hurricane Spin, the Magic Cape, etc. Beating them was purely for bragging rights (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 Puzzle Boss: whenever it gets decapitated, Link must swat the head back to its own body to make Blind vulnerable again.
    • The Updated Re-release of The Legend of Zelda: Link's Awakening for Game Boy Color featured a Bonus Dungeon 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.
    • The Legend of Zelda: Spirit Tracks has Dark Link at the end of Take 'Em All On's final level.
    • The Legend of Zelda: A Link Between Worlds: Once you've completed all the StreetPass challenges, you're able to fight the bonus boss of that game. 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.
    • The Legend of Zelda: Breath of the Wild:
      • Lynels 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 basic enemy in the game, and for a while the most powerful variant, the 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 scale up to Silvers. Master Mode of the game introduces an even stronger version of the Lynel, the 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. 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 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.
  • Ōkami has the Bandit Spiders and the Kusa Five.
  • Tribal Hunter 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.

    Action Games 
  • In ActRaiser 2, enter the password "Xxxx Yyyy Zzzz" to fight the final boss from the first game with the second game's mechanics, who takes several steps up in difficulty from the first game, as well as the final boss from the second.
  • Cave Story has G-CLONE, fightable in the removed Wind Fortress that was restored in the Steam and 3DS eShop versions as a bonus area.
  • Metroid: Other M has the Metroid series's first bonus boss. If you play the post-credits sequence for 100% and the extra ending, you have to butt heads with 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 Playable Epilogue), the Phantoon fight was intentionally left out of Hard Mode.

    Beat 'em Ups 
  • Via Asura's Wrath DLC, two Bonus Bosses that have nothing to do with the main game story are Ryu and Akuma, who become Evil Ryu and Oni respectively.
  • 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 Jubileus. What? You say he just looks like Balder with a Scary Black Man makeover? Well, consider this: Balder didn't have Wicked Weaves. Not only that, but regardless of what difficulty you've been playing on, the Rodin fight is automatically set to 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, good luck.
    • Beating all Alfheim challenges unlocks Angel Slayer, with a boss fight against another Bayonetta. Mechanically she's similar to 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.
  • Bayonetta 2:
    • 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 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 Turns Red and becomes The Infinite One.
    • The Brutal Bonus Level of this game, the Witch Trials, ends with two Dual Boss 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. 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 Dungeons & Dragons Beat Em Ups.
  • The doujin game Grief Syndrome has Oktavia von Seckendorff, an optional sixth witch who can be fought at any point as long as Sayaka is dead. This already-difficult fight is made harder by the fact that you can't use Sayaka, who is generally considered the best character, against her — as anyone who's seen Puella Magi Madoka Magica to the end knows, Oktavia is the result of Sayaka becoming a witch.
  • No More Heroes 2: Desperate Struggle has Kimmy, a school girl with an 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 River City Ransom, Benny and Clyde are the only bosses that you don't have to defeat in order to access River City High School. Once inside, you can also skip Tex as well, since only Otis has to be defeated in order to fight the Dragon Twins, and then Slick, who is actually Simon.
  • In Senran Kagura (Burst), after defeating the final boss, you have the opportunity to fight a sixth playable character for your chosen faction (Daidoji for Hanzo Academy, and Rin for Hebijo Academy). In order to win the mission and make them playable, you have to defeat the boss with all five of your other characters in succession, without losing.
  • 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 Yakuza 0, a quartet of massive 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, bears and tigers, and real-life professional wrestlers.

    Card Games 
  • Yu-Gi-Oh! Reshef of Destruction:
    • 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.
  • 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).

    Fighting Games 
  • BlazBlue:
    • BlazBlue: Calamity Trigger the only way to fight Unlimited Ragna is to go through Score Attack Mode or to play through arcade mode finishing each opponent with a Distortion Drive (the True Final Boss method). Continuum Shift: Extend features "Abyss Mode", where a special version of Unlimited Ragna appears at 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.
    • 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. Central Fiction replaced this with Grim of the Abyss mode, which is effectively the same thing.
  • BloodStorm had several of these, all of them Palette Swaps of your main characters. Unlocking most of them was both fun and 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 Bloody Roar 3. To reach her, the player must win every fight without losing a single round; which includes the fight against Xion. If successful, Uranus will appear immediately afterward, however, this also represents the Point of No Continues. Meaning, if you lose, it's an automatic Game Over. So you only get one chance to try to defeat one of the most broken fighting game characters EVER.
  • 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 The True Final Match after your next match.
  • Fatal Fury:
    • 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, Fatal Fury Special had a Bonus Boss in Ryo Sakazaki, who was the first seed in the long running franchise known as The King of Fighters.
    • Finally, Alfred Airhawk fills this role in Real Bout 2.
  • The final boss of the story mode in Dissidia Final Fantasy is Chaos, who is only level 50 or so and thus can be defeated easily with Level Grinding. 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 One-Winged Angel, Feral Chaos. Your reward for beating him? The ability to play him.
  • Baiken, in the original Guilty Gear 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 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 The King of Fighters: Maximum Impact Regulation A without using any continues and with enough Super Finishes, you'll get to fight Makoto Mizoguchi of Fighter's History fame.
  • Lightning Legend: Daigo no Daibouken has two of them, Girigiri Oyaji (the game's Mr. Exposition and sponsor of the All There in the Manual national fighting tournament) and K.O.J. (the current champion of said tournament). You'll fight them after the Final Boss, if you have finished the game with all regular characters, then did a No Continue Run (and for K.O.J., you need on top of that to gather one hour's worth of matches) beforehand.
  • Mortal Kombat is the Trope Maker:
    • The first game has Reptile as a secret boss. There is 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 Double Flawless on your opponent, and finish them with a Fatality. Furthermore, 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.
    • Mortal Kombat II continued the tradition with Noob Saibot, Jade, and Smoke. Noob Saibot appears only if you win 50 battles consecutively. Jade appears if, on the fight before the question-mark box, you only use the Low Kick button to defeat your opponent (can be done on any round). Smoke is the most difficult to get, as you have to make Dan Forden appear and say "TOASTY!" while fighting on the Portal stage, then hit Down + Start while he's on the screen.
    • Mortal Kombat 3 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.
  • One Must Fall 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 Persona 4: Arena, it's possible to unlock a special bonus match against Elizabeth from Persona 3. 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 One-Hit Kill attack on you and be done with it.
  • Punch-Out!!:
    • The Wii game has Donkey Kong. 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 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 True Final Boss); the circuit itself has to be unlocked by winning the first three circuits (Minor, Major and World) without suffering a single defeat.
  • Samurai Shodown 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 Soul Calibur III, 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.
  • Street Fighter:
  • Acceleration Of SUGURI X-Edition has Sora, the protagonist of 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.
  • Super Smash Bros.:
    • Melee has Giant Kirby, who appears in the fifth stage of Adventure Mode if the group of smaller Kirbies is beaten in 30 seconds or less. Giga Bowser also appears as a bonus boss if you clear Adventure Mode quickly enough; and while he fights exactly like Bowser, aside from being bigger and stronger, you can't grab Giga Bowser to throw him off the stage.
    • In Brawl, extra doors appear in three stages after you beat Tabuu; going inside them will pit you against Toon Link, 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 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.
  • 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 Moveset Clone Alex, who is a dinosaur.
  • In Tekken 6, there's Nancy. She's one of several giant robots developed by the Mishima Zaibatsu, perhaps to combat Azazel, who is finally free after 10,000 years. Her appearance is sort of a Big-Lipped Alligator Moment 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. She is playable, but only in one level of Scenario Campaign.
  • Vampire Savior has Oboro Bishamon, the man himself, rather than the armor. Darkstalkers 3 makes him playable.
  • The Virtual-ON 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, 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, 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, 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.
  • Waku Waku 7 and Galaxy Fight, the two fighting games made by Sunsoft for the Neo Geo, shared a common bonus boss named "Bonus-Kun", a punching bag (from "the Punching Bag Planet") with a limited moveset who parodies Ryu. In Galaxy Fight, 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.
  • Way of the Warrior has a hidden contender named Gulab Jamen who 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.

    First-Person Shooter 
  • Borderlands 1 has some in the optional side quests, some of which, like Mothrakk and Marley & Moe, can reach That One Boss 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 "Secret Final Boss".
  • Borderlands 2 keeps it up with a number of such enemies, with each DLC featuring a new Raid Boss:
    • Terramorphous The Invincible, who is even worse than Crawmerax. To quote a dev: "If you don't die at least 5 times before killing him, then we haven't done our jobs." The name of his quest? "You. Will. Die. (seriously)"
    • Some enemies can evolve in-game to turn into more powerful and resistant (and fully healed) versions of themselves. Most of these are still manageable. Let an Ultimate Badass Varkid evolve? You get Vermivorous The Invincible.
    • Hyperius the Invincible, a mutated, power-mad Hyperion engineer found in the Captain Scarlett and Her Pirate's Booty DLC.
    • Master Gee the Invincible, a Puzzle Boss 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.
    • 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.
    • Dexiduous the Invincible, A secret secret boss from the same DLC, a colossal 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.
    • Tiny Tina's Assault on Dragon Keep has The Ancient Dragons of Destruction, a Wolfpack Boss consisting of four dragons, two of which are capable of leveling up the other dragons and healing.
  • Borderlands: The Pre-Sequel! 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).
  • Mega Man 8-Bit Deathmatch has several in the single player mode:
    • The original version from the beginning had 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. Oh, and the game remembers that you had beaten them, as they appear in a room before the Boss Rush in V5B onwards.
    • In v5, if you defeat Bass in the Mega Man 7 chapter without using the Super Adaptor, you'll be able to fight the Wily Capsule, the original chapter 7 boss that Bass replaced.
    • Also in v5, Quint. To even find him, 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 five gruelling phases to boot with no checkpoints at all if you die at any point. To say nothing of its spectacle: 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 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 Mega Man X 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? A trophy appearing in the basement of Dr. Light's lab.
    • v6 added Ra Thor and Ra Devil in Chapter 13. After finding all the artifacts for Pharaoh Man's sidequest (good luck with that) and making your way through a gauntlet of puzzles, 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 put you through deadlier versions of the puzzles you solved to get to it. Defeating them gives you the Dawn Breaker, a chapter-exclusive Infinity +1 Sword.

    Hack and Slash 
  • Diablo II has some in its later updates. Versions 1.00-1.09 had the Cow King as a sort of Bonus Boss, though he was substantially weaker than the actual final bosses. Version 1.10 introduced Uber Diablo as a new Bonus Boss, and 1.11 introduced the Pandemonium Quest, which involves looking for keys and battling buffed-up "Uber" versions of bosses (Uber Izual, Uber Duriel, and an important lore character Lilith, who is 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!
  • Diablo III has the Infernal Machine update, which introduces four unique bosses, the key keepers, in each act. After obtaining all the keys, the player could craft the Infernal Machine, which allows battling two super-versions of game's bosses at once, for great rewards. There are 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.
  • Dungeon Siege has two. One is easy to find, while the second is extremely hard. The first is Scorch, the ancient dragon of Rathe, whom the player could avoid simply by continuing by the road to Castle Ehb. Scorch is the biggest monster in the game, has the highest number of HP, and is nearly as deadly as the final boss. The second Bonus Boss is located in the hard-to-find secret "Chicken level", amongst the various chickens named after the game's developers. It is 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.
  • Grim Dawn 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 Otogi: Myth of Demons, 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 Homing Projectile? If you had trouble beating the last boss of the game, then The Crimson King will wreck you without mercy.
  • Path of Exile 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 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 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 True Final Boss of the Atlas got added, a Duel Boss 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 Temporary Online Content, 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 Seven Samurai 20 XX: 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.

    MMORPGs 
  • Most MMORPGs have such things: Giant Monsters in City of Heroes, world/raid bosses in Everquest, and raid bosses in World of Warcraft. Some are 'storyline' bosses, of course, but a lot of them are easily skippable.
  • City of Heroes has the Army of Me badge, unlocked via a special option in a Villain Side story arc. The mission? Beat a full team 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.
  • Dragon Nest has several high level maps feature alternative routes with different bosses.
  • Final Fantasy XI has the Notorious Monsters. The most, well, notorious of these are the Pandaemonium Warden, a Sequential Boss with 10 different forms who has to be beaten in 2 hoursnote , and Absolute Virtue, who has such absolutely obscure mechanics that it was never beaten fairly until the rising level cap made it irrelevant.
  • Final Fantasy XIV:
    • The game features plenty of end-game contents, some of which are either Bonus Dungeon 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 pulling all their stops at the get-go compared to regular Coil, culminating with Bahamut Prime dropping 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 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 giant puzzle, as the party needs to hit the Primals with their own attacks to power them up in order to obtain extra Limit Breaks 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 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 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 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 Total Party Kill. 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 Duel Bosses (Gabriel, Beast King Lyon, and 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."
  • 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 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.
  • Guild Wars 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 True Final Boss.
  • Kingdom of Loathing 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 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 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 bugbear made of stars that hits with a variety of powerful elemental attacks, or the Great Wolf 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. There exist Hard Mode versions of the Dreadsylvania bosses, which are even more dangerous but drop even better loot. Good luck finding them without a guide.
    • 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.
      • 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 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.
  • 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 Corporeal Beast; while others are just in a dangerous area, such as the Chaos Elemental. The Final Boss 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 Star Wars: The Old Republic:
    • 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.
  • World of Warcraft 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 Final Boss 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. 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 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 sterilizing the planet to rid it of corruption so that life can begin anew. Also, in-story, it's stated that he could completely and utterly wreck Yogg-Saron in a fight, and the main thing keeping him from actually doing so is that it would 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 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 Guide Dang It! 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.
    • The Cow King showed up in an event to commemorate 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.

    Platform Games 
  • Duke Nukem: Manhattan Project 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 Marathon Boss, 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. Bragging Rights Reward, indeed.
  • Dynamite Headdy has a Bonus Boss called "The Money" that is unlockable with a password you get by beating the bonus game four times.
  • Kirby:
  • La-Mulana's infamous Hell Temple has its own guardian, The Boss (no, not that one), a giant blob with Naramura's (the game ideator) signature face that 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.
  • The Legendary Starfy has Old Man Lobber, who is unlocked by beating all the records in Stage 10. He has Bullet Hell attacks, and a hard to avoid One-Hit Kill move when he gets low on health.
  • The Legend of Spyro: Dawn of the Dragon has Elite Enemies in every chapter. They look like normal enemies with a few modifications. They're not. They're hard to damage, let alone kill...
  • Mega Man:
    • Mega Man (Classic):
      • Proto Man in Mega Man 7, who can be fought in a secret area in Shade Man's level after meeting certain requirements. The reward is his shield.
      • Mega Man 8 had two in the Sega Saturn version, and they happen to be Cut Man and Wood Man from Mega Man and 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.
      • Mega Man 9 has Fake Man, who only appears at the end of a Time Trial stage bought via Downloadable Content.
      • Mega Man 10 features the return of the 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.
      • ROM hack Rockman 4 Minus Infinity 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 No-Damage Run through the entire game (up to and including the first two Chimerabots) has Shadow Man replacing the third and final one by way of Diagonal Cut.
      • Fan game Mega Man Unlimited 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 and also kill Yoku Man in two hits in the Boss Rush later on.
      • Mega Man Revenge Of The Fallen has two of these: Knight Man and Bass, who can also be found in Knight Man's stage in an area that requires his weapon to access, meaning you have to beat the stage twice for 100% Completion.
      • Mega Man Super Fighting Robot has five of these, unlocked by beating the game in different ways: Bass (beat the game on Hard mode); Shovel Knight (beat the game with over 1,000 screws in reserve); Simon Belmont (beat the game with no upgrades); Red Mage (beat the game with all the upgrades; and Dr. Light (beat the game on Insane mode).
      • The Make a Good Mega Man Level Contest 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 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 Pit of Pits, also accessible after the Wily stages, is Galaxy Man in a Free-Fall Fight. Finally, each of the Arenas has one of their own as well. The regular Arena has Quick Man anda souped-up Gamma; the Mega Arena has an army of Volt Men; and the True Arena has Absolute Zero again, this time with a new fourth form.
    • Mega Man X:
      • 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.
      • 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 Infinity +1 Sword. 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.
      • Mega Man X6 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 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.
      • 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.
    • In Mega Man Zero 3, in a secret area in the second-to-last level that can only be opened by going into cyberspace, Zero will encounter Phantom, who died two games earlier, ready to fight him to test his worth as a hero. Victory will net the player the infinity plus one, er, boots.
    • In Mega Man ZX, 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 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 Zero. 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 Model OX, who is — you guessed it, Omega Zero, complete with a crapload of awesome special moves and total badassery. 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 Mega Man Network Transmission, 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 Bass.EXE.
  • Ratchet & Clank:
    • Ratchet & Clank Future: A Crack In Time has Vorselon, Ratchet's father.....'s accountant.
    • In Ratchet & Clank: Going Commando, 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 second and third game of the original trilogy have these in 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 (taking no damage, weapons switching on its own ...) and usually take part in some ultimate challenge consisting of many rounds.
  • The Simpsons: Bart vs. the World: If you collect all the Krusty items, you get to fight Itch and Scratchy.
  • Sonic the Hedgehog 2 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. 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.
  • Super Mario Bros.:
    • Wario Land: Super Mario Land 3 has Hinyari, located in Sherbet Land. Amusingly, you can just walk right out of the battlefield through a convienently-placed door.
    • In the fangame Super Mario World: Piranha Island, there's a secret boss hidden in Darkness Piranha. It is a recreation of the Master Hand battle from Super Smash Bros. in the Super Mario World engine.
    • In the fangame Mario Gives Up, returning to "Area of Bonuses" after pressing all four switches allows you to reach the Key Boss.

    Puzzle Games 
  • The Archivist in DROD RPG: Tendry's Tale. You get a special ending for beating him, which was meant to require saving up the 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).
  • Dr. Mario 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 Vampire Wario; conversely, Wario will have to contend with Metal Mario. Defeating them first try will unlock them in Versus Mode, where they're not only playable but also have the hardest AI.
  • Professor Layton:
    • In 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 Pony Island changes the ending to Hopeless Soul telling you that he now understands that you want a satisfying reward for getting full completion and fighting you in a three-stage boss battle using different gameplay segments to supply that reward.
  • Puyo Puyo: Carbuncle has played this role twice in the series. To wit:
    • 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.
  • Puzzle Quest 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 completionist, an achievement hunter (which you don't even get, depending on the platform) or for the bragging rights.
  • Sutte Hakkun has the Purple Makkun, an odd-colored Makkun that hides within specific crevices in certain stages in every world, serving as the replacement for the 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 a race in one of his ten Battle stages (which have the same level of difficulty as the regular stages). Beat him, and you'll get a segment of the Solution code to write down.

    Racing Games 
  • In any version of Initial D Arcade Stage, defeating all opponents in Legend Of The Streets mode once per loop will take you to a free battle with the game's True Final Boss, Bunta Fujiwara. He is extremely difficult to beat, often sporting Rubber-Band A.I.. Whether or not you defeat him, the credits will roll afterwards.
  • Mario Kart DS 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 Secret Character, and if you win, you unlock them as playable. However, winning these races isn't necessary to complete the game, and mercifully you don't have to win each tournament again to have another shot if you lose. Note that the first two, Cosworth and Tetsuo, defy the usual Bonus Boss difficulty expectations by actually being slightly easier than the Nintendo Hard regular races. On the other hand, the third and final Bonus Boss, Beemer, is 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 Rubber-Banding, Perfect-Play A.I., and the fact that you're racing him on That One Track; an 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 Rage-Quitting.

    Real-Time Strategy 
  • Dawn of War II has two optional missions. One, against the Eldar, has you fight an Avatar of their war god, which is considered to 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 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 Defense of the Ancients. It will fuck up anyone who goes in unprepared, and its destruction is completely unnecessary.
  • Defense of the Ancients: All-Stars and its sequel Dota 2 has Roshan, extremely hard to defeat single-handedly, but defeating it will yield a good boon to the team that defeated it.
  • Heroes of the Storm has either golem-like mercs or various others, depending on the map.
  • League of Legends has Baron Nashor (and Vilemaw for Twisted Treeline map).
  • 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 Hard Mode Filler.
  • From the Paradox Interactive strategy games:
    • Crusader Kings: With the Jade Dragon DLC, Imperial China 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 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.
    • Hearts of Iron: You can use a console command to spawn an Alien Invasion on a province of your choicenote . The aliens 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.
    • Stellaris: Fallen Empires. You don't actually have to fight them (unless you're playing as Fanatic Purifiers or 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.
  • Pikmin:
    • 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, 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.
    • Pikmin 3 Deluxe features a new boss at the end of the "Olimar's Comeback" sidestory: 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.
  • Smite has the Fire Giant (and Apophis for the Clash map).

    Rhythm Games 
  • 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 True Final Boss, usually named either "One More Extra Stage" or "Encore Extra Stage", and is generally the hardest song in the game (and gets progressively harder with each subsequent installment). beatmania IIDX is known for having elaborate Extra Stage systems where, on your Extra Stage, you enter a special screen where you select one of several different boss songs. Completing all of these songs and fulfilling certain requirements on them (often a grade and special gauge requirement) will allow you to unlock and immediately play the system's Final Boss. beatmania IIDX 20 tricoro introduces the "LIMIT BURST" system, which uses crossovers from other Bemani games as bosses.
  • In Bust a Groove 2, getting "Fever Time" in each level lets you face off against Pander, a 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 Butoh and whose stage is a White Void Room with screens displaying seemlingly random black-and-white photographs before turning into an Amazing Technicolor Battlefield. 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 Final Boss, lets you play as him.
  • From DJMAX Technika:
    • In the Specialist set, getting 70% accuracy or lower nets you Fermion SP, a chart riddled with Fake Difficulty 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 Son of Sun SP), you'll probably have to intentionally Do Well, but Not Perfect 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 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 YouTube videos. A hacked mission in Platinum Crew (in celebration of the Mid-Autumn Festival) spat up 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 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 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 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.
  • Frederic: Resurrection of Music 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.
  • Guitar Hero:
    • This bonus level from Guitar Hero III, featuring DragonForce's "Through The Fire And Flames", may be harder to beat than any of the above examples.
    • There's also its predecessor: "Jordan" from Guitar Hero 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 guitar and drums.
  • 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).

    Roguelike 
  • ADOM has quite a lot of these. Most of them reside in a Brutal Bonus Level 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, extremely fast quickling bard Filk, the complete opposite Emperor Moloch, and Keriax the multi-headed chaos dragon, who are all necessary to beat in order to reach the True Final Boss.
  • The Binding of Isaac: Afterbirth, the DLC for the remake Rebirth, provides one in the form of 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 True Final Boss, Delirium. The scoring system encourages fighting Hush for getting a high score in daily runs, as it and the Boss Rush each give out thousands of points on completion.
  • Darkest Dungeon 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 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.
  • Dungeons of Dredmor: The real Final Boss 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 Enter the Gungeon, 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 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 the Lich are the only other bosses with this distinction), with the third and final phase 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 FTL: Faster Than Light, within the Rebel Stronghold sector, there is a huge shipyard. If decide to explore it, you find an unfinished second rebel flagship. It is the 3rd phase of the hard mode Rebel Flagship, but its systems are weaker, it has less crew, no mind control, no power surge, and no AI takeover on crew death. Defeating it delays the Rebel Fleet, grants you a very large reward, and unlocks the Federation Cruiser.
  • Hades: During any run, it's possible to initiate a fight with Charon by "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 Final Boss. However, if Zagreus beats him 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.
  • 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 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.
  • Slash'EM Extended, a variant of NetHack variant Slash'EM, 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.

    Shoot 'em Ups 
  • Abmneshi The Prophecy has, in addition to a collection of True Final Bosses, a secret and entirely optional stage containing Sirisai, who's about as hard as the Final Boss.
  • Armed Police Batrider has a crapton of Bonus Bosses, all of which appeared in the Mahou Daisakusen series and Battle Garegga. Said bosses include Bashinet, the Stage 1 boss of Mahou, and Black Heart, the Stage 5 boss of Garegga that, thanks to the stage edit feature, you can fight as early as Stage 2.
  • DoDonPachi Dai-Fukkatsu has the six normal bosses of DoDonPachi (Suzaku, Senkou, Kakou, Raikou, Rankou and Ryuukou) as bonus mid-bosses, triggered by fulfilling certain conditions.
  • The giant space worm of Event Horizon, which can be randomly encountered in Beacon events. It sends out a Horde of Alien Locusts at the player in addition to normal attacks, and you have to destroy its tail segments before you can deal any meaningful damage to it. The same enemy appears later on as the boss of one of endgame factions.
  • 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 Beam Spammin' Heaven's Gate.
  • Hellsinker, as with Batrider and Garegga, has loads of secrets. Defeating the Scarlet Queen will result in a secret form of the boss that unleashes hell for 15 seconds, then disappears. The secret form can be easily triggered if the player has the game at a high rank, but it can also cause quite a surprise by randomly appearing under normal circumstances. If that happens, you're in for a world of hurt.
  • Finish Gokujou Parodius, and you get to fight your way through a "bonus stage". Who awaits at the end? A fire-spewing laser-shooting warmachine-deploying robotic penguin. It's as awesome as it sounds.
  • In the PS2 remake of Space Harrier, 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 Touhou Project games ever since Story of Eastern Wonderland. Typically, after beating the Final Boss, the heroines once again investigates another, smaller incident in the Extra Stage that is caused by the Bonus Boss.
    • In Touhou Fuumaroku ~ the Story of Eastern Wonderland, the stage 1 boss Rika returns with her newest tank creation, the Evil Eye Sigma.
    • In Touhou Gensokyo ~ Lotus Land Story, the heroine 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 Touhou Kaikidan ~ Mystic Square, the stage 3 boss, Alice, returns for a revenge match using powerful magic from her undealed grimoire.
    • In Touhou Koumakyou ~ the Embodiment of Scarlet Devil, after storming the Scarlet Devil Mansion to beat Remilia Scarlet, her younger sister Flandre Scarlet is kicking up a fuss and you need to return there and stop her.
    • Touhou Youyoumu ~ Perfect Cherry Blossom 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.
    • Touhou Eiyashou ~ Imperishable Night, 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 Touhou Fuujinroku ~ Mountain of Faith, 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.
    • Lampshaded in the 11th game, Touhou Chireiden ~ Subterranean Animism. When playing as the Marisa/Alice combo, there's a conversation along the lines of: "Why are we here again? We already beat the final boss." "It's the Extra Stage, just do it." The page quote is the start of that conversation. Story-wise, you heard that the ones empowering 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 Touhou Seirensen ~ Undefined Fantastic Object, you discover that Byakuren's crew are completely clueless about the UFOs floating around, so this time you go and meet the real culprit, Nue Houjuu.
    • In Yousei Daisensou ~ Touhou Sangetsusei, 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 Touhou Shinreibyou ~ Ten Desires, Mamizou Futatsuiwa is supposed to be a reinforcement against Miko, but you've already beaten her. Mamizou then challenges you for a fight, anyway.
    • In Touhou Kishinjou ~ Double Dealing Character, most 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 Touhou Kanjuden ~ Legacy of Lunatic Kingdom, 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.
    • Touhou Tenkuushou ~ Hidden Star in Four Seasons shakes things up a bit. Canonically, you lost against the Final Boss 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 Final Boss and Bonus Boss are the same character in Touhou.
    • In Touhou Kikeijuu ~ Wily Beast and Weakest Creature, Saki Kurokoma, one of the leaders of the Animal Realm, took advantage of the power vacuum created after you beat Keiki and launched an invasion to neighboring realms. It's up to you to stop her.
    • In Touhou Kouryuudou ~ Unconnected Marketeers 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.
  • 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.

    Simulation Games 

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

    Stealth Games 
  • Metal Gear Solid: Peace Walker has the mock battle with Metal Gear ZEKE, souped up versions of the military vehicles and AI weapons, custom versions of these bosses, and all of the Monster Hunter bosses.

    Survival Horror 
  • Fatal Frame 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.
  • Five Nights at Freddy's 4 has Nightmare Mode, which involves you facing off against a scarier, smarter, and all around more intense Fredbear aptly named "Nightmare".

    Third-Person Shooter 
  • Lost Planet: 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 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.
  • Splatoon 2's Octo Expansion has Inner Agent 3, accessible after collecting all of the Mem Cakes. Appropriately, the framing device is Agent 8 reliving their memory of fighting Agent 3 in the first game. It's a fairly difficult five-phase fight with Checkpoint Starvation, 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 Golden Toothpick headgear for multiplayer battles.

    Turn-Based Strategy 
  • Final Fantasy Tactics gave us Elidibs and the Zodiac summon.
  • In the Fire Emblem franchise:
    • In Fire Emblem: Genealogy of the Holy War, in the Final Chapter, Areone is flying around with a squad of Wyvern Knights. However, the chapter can be cleared without ever fighting him, and he'll even become an NPC ally if Altenna talks to him.
    • Fire Emblem: Path of Radiance 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 Final Boss, Mad King Ashnard. If you take him on and take him out, you can loot the most powerful lance in the game, the Wishblade. It is, however, entirely possible to avoid fighting Bryce by taking another route.
    • Fire Emblem: Radiant Dawn has Levail, General Zelgius's apprentice and Bryce's successor as the wielder of the Wishblade. While Ike fights a Duel Boss 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, Anna herself serves as this in Fire Emblem Awakening's hardest DLC map. Outside of DLC, there's Spotpass character 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 everFor Reference... . 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 Fire Emblem Gaiden, 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 a young version of Grima, the main antagonist of Awakening.
  • Luminous Arc 2 has the reoccurring boss for the optional That One Sidequest Spa Battle series, Vanessa. Not only does she have high strength and can use a stat-boosting spell, she's also joined by respawning and stat-specialised 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 Flash Drive. She'll get stronger each time you face her, until the sidequest is finished. Beating this multiple of times with New Game Pluses is required for the 100% Completion.
  • Nippon Ichi games:
    • Demon Supreme Overlord Baal in the Marl Kingdom series, La Pucelle Tactics, Disgaea, Phantom Brave, Makai Kingdom, 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 Disgaea: Hour of Darkness are all Bonus Bosses in Phantom Brave, 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 Disgaea 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.
    • 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 (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.
    • Phantom Brave and The re-release of Disgaea 2 brought back Mythology Gag 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 Disgaea 4 as the final bonus boss.
    • Disgaea Dimension 2 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 Marathon Boss.
    • 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 Telepath Tactics, an extremely high-level swordfighter wielding an Infinity +1 Sword. 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 the previous game, you are expected to run from her, but it is possible to beat her, either by prior Level Grinding or by abusing terrain damage.
  • In the postgame of Yu-Gi-Oh! Monster Capsule GB, 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.

    Visual Novel 
  • Lux-Pain zigzags between this and Skippable Boss. 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.

    Wide Open Sandbox 
  • By the same token, nothing in Dwarf Fortress says you have to find the Hidden Fun Stuff. Or 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 Minecraft are optional. The first is the Enderdragon, which doubles as a Final Boss. The second, more traditional example, is the Wither, which has to be summoned by completing a difficult task, is insanely hard, and drops the Nether Star, which can only be used in constructing Beacons, devices which give you bonus abilities.
  • Terraria:
    • King Slime's main purpose is giving the cosmetic 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 Final Boss and drops a lot of good stuff, but is comparatively hard to summon and doesn't advance the world at all.
    • The Empress of Light is an optional Bullet Hell 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.


 
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Alternative Title(s): Super Boss, Secret Boss

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The Enigmatic Man

The Enigmatic Man, a strange and haunting presence found in Hollow Bastion.

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