True Final Boss

You're showing off how awesome you are at a game. You might be on a harder difficulty than you usually play. You might be playing the whole game without getting hit. You might even be playing the game blindfolded. (Okay, probably not.) Regardless, you get to the Final Boss, unleash complete destruction, and defeat it without much effort. You put the controller down, ready to watch the ending...

...and then frantically pick it up again when a new boss comes out of nowhere and starts kicking your ass. Huh? Where did this guy come from?! You don't know why this boss never showed up before. Maybe you had to be at the hardest difficulty level. Maybe you're doing much better than you were before. Maybe you completed a Sidequest that didn't necessarily let you know this was going to happen as a result. Regardless, you have now run into the True Final Boss.

Expect lots of death, wailing, and grinding of teeth, as these bosses are typically much more difficult than every other boss in the game (unless one of them ends up being That One Boss). If you haven't had trouble up until then, you will suddenly see a massive jump in difficulty when you start fighting the boss.

This can also be annoying if the Game guide intentionally fails to mention this boss.

Compare Final Boss, which it is by definition, and That One Boss, which it will usually become. Also compare Bonus Boss, as by definition the True Final Boss is technically optional (however, do not confuse the two). May be The Man Behind the Man, or just the original final boss's One-Winged Angel form, or a Giant Space Flea From Nowhere. Can also overlap with Bait and Switch Boss if the True Final Boss replaces the normal one.

If the reward for beating this guy isn't the Golden Ending (or some sort of huge bonus feature), there will be great rage. Indeed, if beating the standard Final Boss nets you some sort of Downer Ending, Bittersweet Ending, or Gainax Ending, nine times out of ten, there's a True Final Boss waiting in the wings that you'll have to uncover and defeat to get a happy ending that provides some sort of closure to the story. (This goes double if the game was lighthearted up until everything went down the tubes at the "end".)

'''These examples are pretty much all spoilers. Read at your own risk.'''

Action Adventure

 * Ganbare Goemon 3 lets you fight the recurring Kabuki if you collect all the health power-ups.
 * If you get the Tsubaki Mark III in No More Heroes, you get to fight.
 * In Oracle of Ages/Seasons, there is a multi-stage final boss at the end of each game. If you beat one and then transfer your save file to the other via code or wire, you get to see new things. One of these things happens after you beat the final boss of the new game. Zelda comes to you, and is promptly kidnapped by Twinrova, who then reveals that the first two final bosses were just sacrifices to bring back Ganon, and Zelda is the final sacrifice. Cue two insanely hard battles against them.
 * The SNES version of Sparkster has this. When you play on Hard, instead of the Final Boss dying before he launches the missile, he dies right after he hits the button. Guess what the True Final Boss is this time? And it really is deserving of That One Boss, as even the mecha battle against Axel Gear seems easy compared to this boss.
 * When playing a higher difficulty in the Genesis version, you fight a 2nd form of Gedol.
 * In Bomberman 64, a player who has gotten every Gold Card and "flawlessly" defeats Altair will get to see reveal himself as one of these, vaporize Altair with a Wave Motion Gun, and dare you to come after him.
 * The arcade version of Golden Axe ends when you beat Death Adder. When you beat him in the Genesis version, it lets you think the game is over... and then cheerfully informs you that you have to fight Death Bringer now.
 * Collecting all the 65 weapons in Drakengard unlocks a 5th secret ending in which you fight . Though it's a rather unconventional battle, more akin to a Rhythm Game than to a real boss, it is widely considered the hardest challenge in the game by far.
 * In Nie R, the true final boss for Endings C and D is, who is unlocked in your third playthrough.
 * Clearing every Grudge Match in Custom Robo Arena (which in turn requires beating the game and reaching Hundred-Percent Completion) unlocks two more fights; a rematch against, and after that, a fight against.

Dating Sim

 * In Mitsumete Knight, you get to fight the leader of the enemy army, Wolfgario the Ravager, in his unmasked version if you have killed all the Generals who have appeared before him during the game. He's not more powerful than his masked version, but still follows this trope well, as his defeated animation in battle is different: instead of just dropping his sword and standing, contracted in pain, he now holds out his arm towards the sky, gets shocked by a thunderbolt, and falls on the ground.

Fighting Game

 * If you play the Story Mode in Soul Calibur 3 normally, the Final Boss will be Abyss, but if you find the path to Olcadan and defeat him without ever continuing instead, you'll get the dreaded Night Terror as your final opponent.
 * Akuma is a popular True Final Boss in the Street Fighter games, first appearing in Super Street Fighter II Turbo to take out usual final boss Bison in one shot and then take you on if you beat every previous opponent without losing a single match.
 * Street Fighter IV moves it up a notch, having Akuma as a true final boss, then the harder to reach Gouken as the true true final boss.
 * Super Street Fighter IV turns them into their Shin forms, making them MUCH harder. And the Arcade Edition adds Shin Evil Ryu and Shin Oni into the mix.
 * Contra: Shattered Soldier has two true final boss fights. The first, if you complete the first five missions with an A ranking, is a Sequential Boss fight with the "Relic of Moirai", then if you manage to achieve and maintain an S ranking through there, you get to fight his Very Definitely Final Form.
 * In the first Bushido Blade, to get the True Final Boss, you had to not get hit at all. There was a way to skip most of the opponents by running to a certain area of the map, take your opponent's legs out so they can't follow you, and jump down a well, which makes you fight only one more opponent before going onto the bosses. You still have to avoid getting hit to get the "real" ending for each character.
 * The flash game Amorphous sometimes surprises you with a Razor Queen instead of the annoying-as-fuck regular Queen. The game's normal "boss", the Queen, is nimble, has the ability to spawn other Queens (via a hostile takeover of another blob), carries two unbreakable claws to your one sword, is smart enough to avoid your swings, and can be beaten samurai style. The Razor Queen, on the other hand, is a colossal scorpion-looking thing with four huge claws that has an annoying penchant of turning you into Ludicrous Gibs. Beating her does unlock the Infinity+1 Sword (one of her claws), though there's not a lot you probably still need it for by this point.
 * The "Master Program" in Battle Circuit. You have to finish the game in one credit or get a high enough score.
 * Super Smash Bros Brawl parodies this trope, actually naming the second-to-last event match "The Final Battle" (Versus Bowser, Ganondorf, and King Dedede) and the actual last match "The Final FINAL Battle" (Versus Snake, Sonic, and a GIANT Mario).
 * A similar playful use occurred in Melee, where the second to last event was "Final Destination Match", which is a battle with Master Hand and Crazy Hand. The last match, "The Showdown", is a battle with Ganondorf, Mewtwo, and Giga Bowser (which Brawl's "Final FINAL Battle" is referencing, with the Giant Mario as Giga Bowser, and Snake and Sonic as Ganondorf and Mewtwo).
 * Also played straight in Melee and Brawl with Crazy Hand, who will only appear if the difficulty level is set high enough and certain other conditions are met. Melee's Adventure mode had similar conditions for fighting Giga Bowser. Beating him earns you a trophy and the sight of Bowser's Adventure Mode trophy actually falling into the abyss, then exploding into a million tiny fragments.
 * In Fatal Fury 3, you could only face the Jin Brothers if you had a high enough score after beating Yamazaki. If you made it to Chonshu, you could only fight Chonrei if you had a grade of B or higher after beating Chonshu. Otherwise, you get the Bad End. In Real Bout Special, if you had a score of over 750,000 after beating Wolfgang Krauser, Geese Howard appears to challenge you in a special "Nightmare" battle. If you lose to him (which will happen quite often), it's Game Over. In Real Bout 2, get a high enough rank and/or beat Geese and Krauser without losing a round and you fight... Alfred, the protagonist of Dominated Mind. Many consider him to be an Anticlimax Boss, since his appearance is just a tie-in to a PS1 port of Real Bout Special that never left Japan. In Mark of the Wolves, Kain R. Heinlein only appears if you have a high enough grade after beating Grant.
 * Fatal Fury Special one ups this. Beat Krauser without losing a round and you fight Ryo Sakazaki. Likewise, Art Of Fighting 2 has a younger Geese Howard as a secret final boss.
 * The King of Fighters loves this one, too. Beating Krizalid with a high enough score in '99 let you fight Iori or Kyo, and in 2002 Unlimited Match, beating Krizalid, Clone Zero, Original Zero, or Igniz lets you fight Omega Rugal if you meet certain conditions. You only get one chance to beat him, and that is literally almost impossible unless you absolutely know what you're doing. Omega Rugal's stats are artificially increased to the point where one normal attack on them does roughly 1/3 of its normal damage. Basically, teamwork is key. Lose one set and it's Game Over. Win and you unlock them for regular play.
 * A variant of this existed in 97 wherein playing as the Hero team, if Kyo was the one that finished Orochi off, you'd go to a bonus battle with Iori.
 * In 2003, depending on how you defeat Kusanagi, you fight either Adelheid or Mukai.
 * And finally, XIII. If you get to the final team battle without enough points, the bad ending plays where it's hinted Saiki rewinds time and tries his initial Orochi resurrection plan again. Getting there with the right amount takes you to the final fights with Saiki and Dark Ash.
 * If you beat I-no in Guilty Gear XX Slash or Accent Core without continuing, and getting at least 10 Overdrive finishes, she creates a portal and transports you to the past, where you fight... Order Sol, an alternate version of Sol Badguy that wears Ky's jacket and doesn't use his trademark Fireseal sword. The character is available from the start, but the CPU Order-Sol is faster, stronger, and regenerates his exclusive charge meter. Not only that, he has an exclusive super move called Flame Distortion which is basically his normal Dragon Install on steroids. It regenerates his health faster than I-no, increases his power and speed even further, and gives him an unlimited super meter and charge meter. And it lasts for double the time of a normal Dragon Install (15 seconds). Oh, and you can't continue against him -- lose and it's an automatic Game Over.
 * Your score determines your final opponent in Capcom vs. SNK 2 Mark of the Millennium. If it's too low, the game stops after the last team match. If it's in the middle, you fight either Akuma or (on a higher score) Rugal. A higher score than that gives you Shin Akuma instead, and if it's higher than that, you fight God Rugal. Note that the SNK bosses are your rewards for higher scores... (If your score is high enough after the third team, incidentally, you get a midboss fight - either M. Bison or Geese Howard.)
 * Under ordinary circumstances, Battle Arena Toshinden ends with a generic "you win" message following the defeat of Gaia. But if the player makes it all the way past Gaia on Hard difficulty or above without losing a match, the battle with Gaia is followed by a battle with Sho, followed by a character-specific ending after Sho is defeated.
 * Digimon Battle Spirit has a partial example: Fulfilling certain conditions would cause Impmon to replace the Digimon you were supposed to fight beforehand, which acts as an SNK Boss (complete with power-nerfing as an unlockable). However, he doesn't entirely fit the trope because he's a midboss, not a final boss. The trope was more properly done in the Japan only expanded version. If you get to Milleniumon and beat him without losing once, it'll transform into ZeedMilleniumon.
 * In the PlayStation 2 version of Virtual On, if you beat all 8 mechs in under 15-25 seconds, you will fight the original version of Fei-Yen. This version of Fei-Yen is always in Hyper Mode, but with no downsides and increased stats.
 * SNK vs Capcom: SVC Chaos had 2 true final bosses: A goddess version of Athena from the old Athena arcade game, and Red Arremer from Ghouls 'n Ghosts. Failing to meet them would give you a generic, text-only ending stating your character was never seen again.
 * And you only get one shot at these final bosses. If you lose, then your character gets transformed into something which varies depending on whether you fight Athena or Red Arremer before giving you the generic, text-only ending.
 * In the NES version of Double Dragon II: The Revenge, the final stage (which is simply the final boss battle) is only accessible on Supreme Master mode, the hardest difficulty setting. The Warrior mode ends the game on the penultimate stage (after the battle against the doppelgangers), while Practice only lasts the first three stages. This doesn't apply to the Famicom version, in which the entire game could be played on any of the three settings.
 * If you clear Arcade Mode in Blaz Blue: Calamity Trigger with 10 or more Distortion Finishes and no rounds lost, you get the displeasure of fighting Unlimited Ragna, who has triple health and permanent Blood Kain.
 * And in the console versions of Continuum Shift, beating Hazama with the right amount of Astral Finishes and without losing a round rewards you with a fight against Mu-12. Unlimited Mu-12 that is. If you're using Mu in CS 2 though, you fight Unlimited Ragna instead.
 * Every time you clear the story mode of The Bouncer, you can play through again with your built-up characters. After three or so rounds of this, the game figures you're strong enough to take on
 * You actually fight him three times. The first time, he ties a hand behind his back and still hits pretty hard. The second time is the final boss fight, and he's pretty tough. The third time, as the True Final Boss, he decides he doesn't need to hold back at all, and will easily pummel you with moves you haven't seen before.
 * Touhou has two of these in its first Fighting Game side story Immaterial And Missing Power. With only two exceptions, each character's story mode lets you fight Yukari if you beat the previous five stages without continuing, and then lets you fight Suika if you don't continue against Yukari. (If you don't fight Yukari you get a bad ending, and if you beat Yukari but don't fight Suika you get another bad ending). Naturally, the two characters without True Final Bosses are...Yukari and Suika.

JRPG

 * Kingdom Hearts: Birth By Sleep has three scenarios for the three main characters, each scenario has its own Final Boss. The True Final Boss, though, is fought in the Final Episode (accessed by collecting all off the Xehanort reports throughout the three scenarios)
 * Final Mix takes it a step further with the Secret Episode.
 * The Super Robot Wars games that feature "skill points" - optional challenges in each level - often have a harder final boss as a "reward" for completing most or all of them. Examples include Septuagint in Original Generation, Stern Regisseur in Original Generation 2, and the unholy powerful Neo Granzon in Alpha Gaiden.
 * Also, in Impact, you fight Char Aznable in his Sazabi if you get 50 skill points out of 99.
 * Alpha 3 gives you the Final Boss of Alpha 2 as a friendly reinforcement. Note that the Alpha 3 reinforcement is full-powered. No Redemption Demotion degradation. Under the player's full control. It has more HP than anyone so far has bothered to try to find out, and is essentially unkillable.
 * Super Robot Wars W gives you the "true" ending on a second playthrough, including piloting the true final boss, guarded by four copies of the previous final boss, and  showing up to help you.
 * Super Robot Wars Z 2 has a variation -- if you reach the final boss with enough Skill Points to be on Hard Mode, you are given the option to fight him at level 99 instead of his standard level 70.
 * Shin Megami Tensei Nocturne had a fight like this against the Biggest Bad of them all, . You have to complete the optional (and extremely hard) Labyrinth of Amala dungeon to fight him. Ironically, his entire justification for the fight is to prepare you for a war against an even bigger Big Bad:.
 * Persona 4 does this twice. At first, it looks like the final boss is, eventually you discover that the true final boss is . But , it turns out the true mastermind behind everything is.
 * The Mega Man Battle Network games have SP versions of the main boss replace the normal ones after conditions are met, generally requiring that beating the True Final Boss is the only thing left needed to achieve One Hundred Percent Completion.
 * The sequel series Mega Man Star Force recently switched this up on us: the True Final Boss of Star Force 2 comes after the SP version of the final boss. It's a fiendishly difficult super-version of The Rival.
 * Star Force 3 just gets weird with this. As normal, getting every star lets you fight the super form of the final boss. However, inputting secret passwords lets you fight your Rival's new super form, and the super forms of the Bonus Boss, the Bonus Boss of the last game, and one of the new bosses. After all of that, you can fight the final boss's super SUPER form... as a random encounter. Not only that, but if you go through a long gauntlet of Wi-Fi matches (which is hard with all of the D Cers), you can fight yet another secret boss and earn a secret star.
 * In Fire Emblem Elibe: Sword of Seals, defeating Big Bad King Zephiel with all the gaiden chapters completed and all legendary weapons intact unlocks a few extra chapters, pitting you against The Remnant and culminating in the real final boss fight with Zephiel's literal Dragon, still under orders to carry out his ultimate plan.
 * In Mystery of the Emblem, if the player has all legendary weapons intact and Sirius is alive, Marth finds out that his quest to defeat Hardain was just a distraction so Garnef could revive Medeus.
 * Path of Radiance has something of an anticlimactic final boss on Easy and Normal mode, but he springs a cruel surprise on Hard mode: not only does he start moving (with a massive movement range of 10 spaces), after you "beat" him, he immediately invokes a dark god and resurrects with wildly increased stats and fully-replenished (and jacked-up) HP. And it's still your turn, meaning any units that attacked him are unable to act until your next turn! Adding to that, maybe five characters can actually inflict damage on him before he resurrects. (Eagle-eyed players might suspect something is amiss going into the final chapter, as there are less enemies on the map than in Normal mode.)
 * Final Fantasy XII: Revenant Wings makes the Final Boss and The Dragon level 99 if you have 100% mission completion. Have fun Level Grinding.
 * Similarly in Final Fantasy VII, Safer Sephiroth's HP depends on a variety of things, increasing 30,000 HP for each character at level 99, and increasing 80,000 HP if you cast Knights of the Round on JENOVA.Synthesis. Fortunately, his health is also decreased slightly for every time you killed the head while fighting Bizarro Sephiroth. Ultimately, his health, normally 80,000 HP, can range from 55,100 to 400,000.
 * In Pokémon Gold and Silver (and the Remakes), Red, the main character from the previous games, becomes this. You only meet him after getting all the Kanto badges (which only become available after beating the normal final boss) and going to Mt. Silver. After you defeat him, you get the second "ending", and the credits roll.
 * Tales of Graces -- the Final Boss of the original "main" game was . However, the "Lineage to the Future" makes the True Final Boss be.
 * Tales of Innocence also threw people for a loop when people played the remake. The DS version ends with Mathias transforming into an Eldritch Abomination combining three of the protagonists' past lives. However, the remake version has her suddenly get back up and transform two times.
 * Tales of Vesperia features the sidequest variant. In order to attain the ending, all you really have to do is just beat Duke and Duke in his One-Winged Angel form. However, if you grab all the Fel Arms, all of a sudden, when you beat Duke's One-Winged Angel form... prepare to say Oh Crap as the game will now conclude with its version of Nebilim.
 * In Star Ocean the Second Story, doing a seemingly totally random Private Action will release the "limiter" on the final boss, jacking up his stats and making him nigh-impossible to beat without ridiculous level grinding in the bonus dungeon.
 * Baten Kaitos Origins typically ends with a slightly anticlimactic (but still stupidly hard) battle against . If you defeated a certain optional boss, though,.
 * Romancing SaGa: Minstrel's Song has an optional True Final Boss. If you manage vastly increasing his powers. The jump in strength for each stone beyond the fifth gets larger and larger, and the jump to the tenth is what makes 10FS Saruin a True Final Boss.
 * Mana Khemia Alchemists of Al Revis. The Final Boss is . The only way to fight the True Final Boss is to . The latter (italicized to avoid confusion) given "physical form" is the True Final Boss.
 * In the first Breath of Fire game, is one of these, only occurring if.
 * Disgaea 2: Cursed Memories has a rare example of this (rare for the series anyway, which tends much more towards Bonus Bosses) if you go for the Worst Ending. Upon defeating Zenon, you end up fighting who is at level 2000. (Compare with the previous fight with an enemy at level 90.) And unlike the other storyline fights with enemies at this level, you're supposed to win this one. Granted, it'll take a lot of grinding of a sort just to unlock this fight, but it can still catch you off guard. Luckily, there's a way to back out of qualifying for this ending. Which is a good thing, as your reward for victory is some Nightmare Fuel.
 * Disgaea 4: A Promise Unforgotten puts you up against against a different, much higher-leveled final boss if you clear the second to last stage using only the main character at level 500 or higher.
 * In Record of Agarest War, after spending how many hours in the game, you'd think If you unlocked the True Ending route (itself a Guide Dang It), you get to fight off against
 * Taken Up to Eleven in the prequel Record of Agarest War Zero, where the true end (still a Guide Dang It) nets you close to 20 additional boss fights (each progressively harder than the last) before facing the True Final Boss if you played on hard.

Metroidvania

 * Many games in the Castlevania series have bosses that lead to an abrupt ending if you don't meet a specific requirement, such as equipping the right item to see through an illusion (Symphony Of The Night), or reaching an otherwise unreachable boss (Dawn of Sorrow), etc.
 * Dracula has a secret 3rd form in Castlevania: The Dracula X Chronicles that appears only if you rescue Annette (which means you have to save Iris and Terra. Saving Maria is not a requirement). After you beat the 2nd form again, he reverts to his original form and sprouts 6 demon butterfly wings and vanishes. He then proceeds to fire bats, fireballs, meteors, turn into a wolf, and use his own version of Richter's Hydro Storm. It's a lot harder than it sounds.
 * In Cave Story, if you do all the contrived stuff in the alternate route, you'll get one of these after you defeat the Undead Core. It's only made worse by the fact that you can only save immediately after Undead Core and then have to make your way through a Brutal Bonus Level and yet another nontrivial new boss (who can come out of nowhere and still kill you even during his death animation!) before even reaching the True Final Boss. Then, when you reach him, you find out you get very limited HP/missile/weapon recovery, no new save point, and four difficult fights in a row against his various forms.
 * A variation occurs in Metroid: Zero Mission. There's no extra boss, but if you collect 100% of items, the final boss will have roughly three times as much health as it normally does, and its attacks deal double damage.
 * In Iji, after you have beaten the game once, you can use a switch to make the final boss much harder. This is literally done by activating the "make the boss harder" console accessible via teleport right before him. And the game even warns you.

MMORPG

 * In World of Warcraft, the Ulduar raid instance has an extra boss called Algalon the Observer that can only be fought after beating several other bosses in hard mode. Reportedly, he is far more difficult than Yogg-Saron (the normal final boss) and to make matters worse, will despawn if not beaten within an hour of the first try and won't come back until the instance resets.
 * Algalon the Raid Destroyer. He feeds on your tears.
 * As a boss, Yogg-Saron without any keepers was far harder before the recent onslaught of nerfs. Lore-wise, Algalon could wipe out Yogg-Saron and call it a day, but doesn't want to as it could definitely will.
 * Another example happens in the Trial of the Crusader raid, where an NPC starts congratulating the players on completing the Trial... and is rudely interrupted.
 * If you do Bastion of Twilight on normal mode, the final boss is Cho'gall, who was a fairly tough but doable boss. Beat his much more difficult encounter in heroic mode? The raid's not over, now you have to face the heroic-exclusive fight of Sinestra, a much more demanding fight.
 * Other dungeons have bosses only available in heroic mode, such as the new Deadmines and Vanessa Van Cleef.
 * In the Firelands, Ragnaros gains a fourth phase on Heroic, healing to half health and using entirely new mechanics.
 * Storywise, Madness of Deathwing is this. Deathwing is technically two battles, the first battle is on his back and after he is defeated, the aspects assume that's that. However, Deathwing wasn't quite done and is ready to use the final cataclysm.
 * Kingdom of Loathing's final boss is normally the Naughty Sorceress, who has three forms. However, on the Bees Hate You alternate path, her third form is interrupted by the.

Platformer

 * The Kirby games Dream Land 2, Dream Land 3, and 64 keep their True Final Boss hidden until you achieve One Hundred Percent Completion.
 * Kirby Superstar requires you to complete each of its modes, including mini-games, before revealing another mini-game in which you must Run the Gauntlet, defeating every enemy in the game in random sequence, keeping accumulated damage between battles.
 * In Ultra, there's the True Arena, a powered up version of the Arena unlocked after defeating the following semi bonus bosses. These are Here you will face powered up versions of some of the bosses as well as the three mentioned bosses. Once
 * In Kirby 64, not finishing the game with Hundred-Percent Completion and thus the True Final Boss gets you a fake ending cutscene, that is Nightmare Fuel to a lot of younger gamers: The fairy queen secretly smiling a pretty creepy Slasher Smile into the camera from behind her Scary Shiny Glasses, revealing that she's still being possessed by Zero. For many, this was the ultimate motivation to complete the game -- Everybody wanted to erase that creepy scene out of history.
 * You also can not retreat from this battle. If you pause, your only options become the usual continue, and "FIGHT IT OUT!"
 * Ghosts N Goblins series always required you to play through the whole game twice (In one sitting) to get the right weapon to kill the Final Boss, but Ultimate Ghosts 'n' Goblins spiced things up by requiring you to find "magic rings", often hidden in impossible-to-reach places, to open the doors leading to Astaroth first and Hades later (the latter one requiring ALL of the 33 rings).
 * The spinoff series Gargoyle's Quest had two of these in the third game, Demon's Crest for SNES. If you collected every crest and item, the final boss, Phalanx, would reveal a new form far more challenging than the previous ones. If you beat this and sat through the credits, you got a password unlocking an even harder final boss, Dark Demon, who could be defeated for a different ending.
 * Prince of Persia: Warrior Within had a final fight with the Empress of Time if you just made it that far. If you collected all of the nine health upgrades scattered about, you get the Water Sword and it leads to an Alternate Ending that is much more satisfying, fighting the previously unkillable Dahaka. (The following game, Prince of Persia: The Twin Thrones, confirms this to be the canonical ending.)
 * Super Mario 3D Land has Boom Boom and Pom Pom fought halfway through the real final level, which is only accessed once you beat the final Bowser level for the second time.
 * The Queen of Hearts in American McGee's Alice is relatively easy, if you know how to handle her. Her true form, on the other hand, is a bitch.
 * To clarify, you're restricted to running around on a circle of platforms surrounding the monster. Everything's dark, meaning you can only really see a few feet in front of you. The Queen herself uses nearly every method of attack the enemies have used against you - including the freaking boojums!
 * Every 2D Sonic the Hedgehog game since Sonic & Knuckles has had an extra boss battle if you get all of the Emeralds. The main games usually open up a similar final boss battle by beating all of the branching storylines.
 * Inverted in Sonic The Fighters/Sonic Championship. Reaching round 2 of the penultimate boss fight without losing a single round will let you turn into Super Sonic, becoming invincible.
 * Sonic Heroes made you beat all four storylines and collect all seven Emeralds before you could face the final boss.
 * This gets particularly annoying in Shadow the Hedgehog, where there are ten endings that must be seen before the final stage opens up, some of which are pretty tough to reach unless you come through a certain penultimate stage.
 * And the trend continued with Sonic the Hedgehog 2006, where you must complete the three different storylines, each of which had their own different final bosses, to unlock the last episode where the three hedgehog heroes (after the worst level in the game) take on the ultimate final boss.
 * Played with in the 8-bit Sonic the Hedgehog 2, wherein beating the boss of Scrambled Egg Zone (Mecha Sonic/Silver Sonic) with all the Emeralds collected allowed the player to move on to the true final level, Crystal Egg Zone (which has the same amount of Acts as the others), fight the real final boss, and properly save Tails.
 * Earthworm Kim, Earthworm Jim's Jungian anima, who you only face if you collect all the Soup Cans in Earthworm Jim 3D.
 * In a form of Easy Mode Mockery, Mega Man X 8 features as the Final Boss. The True Final Boss can only be fought on Normal and Hard modes.
 * Super Meat Boy has a second, much more difficult battle against Dr. Fetus once you beat most of the Dark World levels.

Puzzle Game

 * Beating the story mode of Dr. Mario 64 without continuing would pit you against Vampire Wario if you were Mario or Metal Mario if you were Wario.
 * In most versions of Puyo Puyo Tsuu, racking up 180,000 points before reaching the final stage, without using any continues, replaces Satan with Masked Satan as the final boss. (The game challenges you to try this if you beat the game normally.) A special ending occurs if you can beat him, but frustratingly not in the Mega Drive version.
 * Tsuu also has a secret reverse example of this if you really go out of your way to suck. If you can manage to beat every opponent on the first floor without scoring enough points to advance to floor 2, you're pit against Masked Satan... and then get thrown out of the tower for sucking so hard. Video here. (Note that this is only possible in versions of Tsuu that require 30,000 points to advance to floor 2.)
 * In Fever, if you are playing Raffine's storyline, the character who replaces Popoi is none other than Carbuncle! In fact,
 * Also, in SUN, if you play the Hard mode, Carbuncle will battle you.
 * In Pokémon Puzzle League, beating the game on Very Hard reveals that Gary wasn't the Puzzle Master -- rather, Mewtwo decided to use his psychic powers to be very good at this game. If you lose, you'll have to face Gary again before getting another shot.
 * Loco Roco 2: defeating the boss doesn't finish the game. After you clean up all of the dirt, an unlikely villain will pop up and result in a gameplay change.
 * If you take the right path in Meteos, you face off against True Meteo, which is really just three Meteos.

Rhythm Game

 * The Guitar Freaks and the Drum Mania series has a hidden and otherwise unreachable track for anyone who gets an "S" ranking on all of the three tracks he played normally.
 * The many Extra Stage songs of the BEMANI series (Dance Dance Revolution, Beatmania IIDX, etc.) almost always require you to score a high enough grade on your last song (or all of your songs). Usually, these Extra Stages force you to play under modifiers that make the song even harder; for instance, Extra Stages in DDR force you to play with the x1.5 speed and Reverse mods, as well as a life meter that doesn't replenish. And in some of these games, this same requirement can be used to reach what is called the One More Extra Stage, or OMES for short; in DDR, this is a fairly easier song in which you fail instantly if you get one Good, Bad, Miss, or NG, and in beatmania IIDX, this is traditionally an even harder song.
 * In Pump It Up Exceed 2, if you get an 'S' ranking on both songs on Remix Station, you get to play a literally impossible song, RAW (which is also the opening theme). The steps, which include quintuple jumps and hitting all 10 panels at once, aren't meant to be played, but spell out a message.
 * DJMAX Technika 's Technical courses have you select three songs, do those songs, then face a boss song (that is not revealed until you get to it). However, clearing the first two stages with at least 95% of your hits being rated "MAX" will bring up an alternate fourth song. For example, the Customizer course's normal final boss is "Son of Sun," and the TFB is "Sin."

Roguelike

 * Pokémon Mystery Dungeon Rescue Team has Deoxys, who can only be fought once every single Pokemon in that game is fought and recruited (the final boss for Story Mode is Rayquaza).
 * In Doom the Roguelike, nuking the Cyberdemon while under the effects of an Invulnerability Sphere will reveal the secret stairs to the next level, wherein resides the Ultimate Evil.
 * This came out of an unintended feature in earlier versions of the game, where nuking the Cyberdemon still counted as a win, despite the fact you just killed yourself. In later versions, this was changed to marking it as a "partial" victory on your record, since you did technically commit suicide. Now, if you want to try to win that way and survive, the True Final Boss is there to make sure you're not just taking the cheap way out. Unfortunately for people actually trying to face the true final boss, you have to get lucky enough to find an Invulnerability Sphere on the level before the Cyberdemon, making it a Luck-Based Mission.
 * In Ancient Domains of Mystery, the goal of the game is to close the Chaos Gate and keep it from reopening. If you have completed a number of obscure and difficult tasks, you may instead enter the Chaos Gate and kill Andor Drakon.
 * And there are 3 Ultra endings that require even more obscure and difficult requirements!
 * The Binding of Isaac has Mom as the final boss in the first playthrough. However, after that, two new levels are added with Mom's Heart as the final boss. After the 9th playthrough, Mom's Heart is replaced with It Lives, a harder variation of Mom's Heart. The Halloween Update adds a new final level that is normally unlocked after defeating It Lives, although there are a few ways to reach it earlier. At the end of the level, you fight The trope then reaches Exaggerated status when you add its Expansion Pack, Wrath of the Lamb, to the mix, since it adds yet another level after that, with yet another True Final Boss.

Shoot 'Em Up

 * Bullet Hell shooters take the cake for this, featuring impossible bosses such as Hibachi the mecha-bee from the Don Pachi series. And to even reach them, you have to play their games with no continues.
 * Touhou has a few examples. In most cases, a level is not playable until certain conditions are met:
 * The second game, The Story of Eastern Wonderland, had a proper True Final Boss with Mima's second form (really third, but you don't fight the first one), which you can only see if you don't continue until then. Interestingly, you can continue at that form, but you get the bad ending.
 * In the fourth game, Lotus Land Story, the last stage and its Final Boss can only be reached if you play on a difficulty higher than easy, and you haven't continued until then. Otherwise, you receive the bad ending. The last stage also prevents you from continuing, period; there's no bad ending, it's just game over.
 * Similarly, the sixth game, Embodiment of Scarlet Devil, prevents the last stage from being played on Easy difficulty and sends you to the bad ending. If you play on Normal or higher, you can still reach the last stage even if you continue (and can continue on the last stage), but you still get the bad ending.
 * Finally for the shooting games, the eighth game, Imperishable Night, has an alternate final stage, with an alternate final boss, that you can only get to after beating the game once with the specific choice of characters. Continuing on the playthrough that unlocks the alternative final stage is fine, but continuing too much gets a Nonstandard Game Over ending. The true final stage itself can't be reached if you continue, and gives you the bad ending if you die on it.
 * It should be mentioned that the unlockable Extra Stages with their Extra Bosses are technically not this trope gameplay-wise, as unlike other examples, the Extra Stage is really selected from the title screen. Storyline-wise, it is debatable and depends on which game is being played.
 * Mushihime-sama Futari one-upped the genre with two consecutive true final bosses which really do have to be seen to be believed.
 * It's also called the hardest video game boss ever, with good reason. There's even a video on Youtube by that name.
 * And thanks to the 360 port being region-free, anyone with a 360 can now experience it for themselves. What, can't even beat the first stage of Ultra? No problem, you can use Training mode to jump straight to the TFB!
 * Black Label ups the ante again with God Mode and its Beyond the Impossible true final boss.
 * Hentai shooter Sentimental Shooting takes this one step further: Finish a stage (any stage) without using your time freeze and without losing a life, and a bonus boss would appear to blow you to smithereens. Level boss stages are the only exception to this rule.
 * DoDonPachi dai ou jou's Death Label mode pits you against not one Hibachi, but two of them. Have fun dying!
 * Hibachi's incarnation in DoDonPachi Dai Fukkatsu puts even Mushihimesama Futari's TFB to shame.
 * It Got Worse: Black Label Daifukkatsu added a new system that rapidly escalates the difficulty depending on how you play.
 * CAVE really outdid themselves in regards to this trope with Daifukkatsu Black Label, which introduces a second True Final Boss (provided certain requirements are met). Basically a literal Turns Red version of Hibachi.
 * Here it is, Zatzusa, the crowning terror of Shump bosses; Touhou players have it easy. Here it is, on Arcade Mode
 * On the 360 Retail Black Label arrange mode, the Ketsui crossover, now you have to fight Evacaneer DOOM on Steroids (now called HIVAC), making the original look like a mid-boss in comparison.
 * Death Smiles added one (Bloody Jitterbug) in Mega Black Label, which required you to access the final stage on rank 999 and not take damage up to Tyrranosatan. If that sounds a bit too easy, that's because the requirement for accessing Hades Castle at rank 999 includes beating both bonus stages... at rank 999. And the bonus stages have to be taken in a specific order, too, otherwise the rank will be back down to standard rank.
 * And in case you're wondering, yes, 1.1 arranged on the 360 version made it easier to reach him by making it only a 1cc requirement (no more ragequitting over getting hit, no more Rank 999, and no more forcing your way through The Gorge). Unfortunately, beating him this way does not unlock an achievement, as the relevant achievement specifically requires standard MBL.
 * Ray Crisis: If you manage to get to and beat the normal Final Boss, Dis-Human, without continuing, you reach the true final boss, Infinity.
 * Giga Wing normally ends after Stage 6 with a Bittersweet Ending in which your character self-destructs to destroy the Big Bad. Completing the first six stages without continues, however, takes you to the true final boss and secures you a better ending.
 * Ketsui Death Label has "DOOM Mode," which lets you fight the True Final Boss, Evacaneer DOOM (no relation) right off the bat. The catch is that you initially fight an easy version of it, and you fight it again and again, with the boss getting harder on subsequent rounds.
 * As implied, the original version also contains Evacaneer DOOM, but in order to see it, you need to beat the first loop of the game without dying or using bombs with a score of a certain cutoff.
 * Of course, this is still not as bad as Evacaneer DOOM in Death Label on Extra mode....yeah they upped him a BIT.
 * Raiden IV has one at the end of the second loop.
 * Freeware shmups are not immune to this.
 * The Light Gun Game Razing Storm has this of sorts -- The third stage has you defeat the terrorist leader, and if you managed to survive the last-ditch Macross Missile Massacre of the Spider Tank, you're treated to the true final stage, a bonus stage of sorts. Where you finally face against a Cool Airship that comes out of nowhere.
 * Andross's Brain in Star Fox 64 and the Anglar Emperor in Star Fox Command.
 * In Every Extend, Heavy mode has a different (replacement, not subsequent) final boss if you collect 7 quicken powerups and 800,000 points. This is doable but not particularly easy, although there's other ways to bring him in the area.
 * In Fraxy, it is possible to make a boss throw out a new form if the rank is 100!
 * In Rez, each of the first four areas has a Mega, Giga, and Tera version of the boss, depending on how well you did throughout the stage. The sudden shift in difficulty is a bit of a surprise the first time.
 * In Tyrian, this actually happens twice in a row; first, you fight a giant brain, after which everything is said to be over, BUT THEN!, the former Big Bad Vykromod appears as a giant nose. If you beat him, the game again states that everything is over, but if you found a certain secret earlier in the game, you now have to fight a minigame-like boss on the planet Soh Jin, which, if you win, is revealed to be a creation of Zinglon himself, who you then fight in an offscreen battle. In Episode V, it's revealed that Zinglon was behind Microsol and Vykromod in the first place.

Stealth Game

 * In Metal Gear Solid Peace Walker, the true final boss will trigger upon completion of Metal Gear ZEKE and finishing all main and extra ops. How difficult the boss fight is depends on how well you obtain the parts for ZEKE.

Survival Horror

 * In Illbleed, there was a hidden final boss that could only be accessed in a New Game Plus, by purposfully not saving your kidnapped friends. Stranger still, every time you let one of them die, Eriko (the protagonist) loses her clothing, until she is eventually completely naked save for a tiny thong-like panty scrap and a couple of band-aids over her nipples. Reach the final arena like this, and instead of introducing the final boss, the announcer will start drooling over you and come down there himself. And believe it or not, it gets even stranger from there...
 * Resident Evil Outbreak has a final boss fight. Your characters run to escape only to be confronted by the boss you just defeated, again. You have the option of blowing him up with whatever weapons you have on hand or injecting him with the cure for the T-virus, which makes him explode.
 * Resident Evil Outbreak File #2 had this one boss follow you throughout the last leg of the finale scenario. Then, if you have to take the long way around to complete the scenario, the game fakes you out by making it seem like you have to fight him again, even if you killed him earlier. But
 * Resident Evil 2 features two in the B Scenario. In the A Scenario, the last fight is against lion-like Birkin, who's tough, but still pretty easy to kill. In the B Scenario, you have to fight, who's much faster than before, hits harder, and can only be defeated by the timely intervention of rocket-based explosives. Then, you reach the end of the story, only to find out that the A Scenario ended prematurely, and you have to fight . Only then will you see the real ending to the game.
 * The true enemy and ending in Parasite Eve can only be accessed by beating the game once, which unlocks the Chrysler Building. Reach the top floor and Aya will confront.
 * Fatal Frame 2 usually ends with a fight against "Rope Man" (aka the Kusabi). However, on Nightmare difficulty on the PlayStation 2 or Fatal difficulty on the Xbox, you fight Sae Kurosawa after him, and get a different, somewhat happier ending.

Third-Person Shooter

 * True Crime: Streets of LA had, based on player performance, story forks that led to worst to successively better endings and another Big Bad. Fortunately, each of these forks were well-written self-contained stories, and had their own unique features that made it worth it to explore each one, and doing so made the True Final Boss appear for the One Hundred Percent Completion ending.
 * Winback plays with this by having you fight the true penultimate boss (Dan) before the normal final boss (Cecile).

Vehicular Combat

 * In Star Wars: Rogue Squadron III: Rebel Strike, while not technically a boss, there is a bonus extension to one level if and only if, you meet the requirements for a silver medal or higher. Earn a bronze medal and the level is finished and you win. Earn a silver or better and you play a short mission in a TIE Bomber and gain an opportunity to unlock said Bomber for use in other missions.
 * Ace Combat Zero plays with this. If you've beaten the game enough to unlock the SP Mission "The Gauntlet" on the highest difficulty, played that mission on said highest difficulty setting, and defeated Espada Squadron in less than 1 minute during the mission, then the game's penultimate boss Wizard Squadron appears. Do you have to fight them, too? Nope, instead a single F-22 Raptor appears from behind them and utterly slaughters Wizard Squadron in all of about 15 seconds. Then that F-22's pilot sets his sights on you. Good luck with Mobius 1, Cipher.
 * Airforce Delta Strike features NAVIGATOR on the final mission for 3rd Element. The only way to get to this boss is by using 3rd Element pilots for almost all of the space-based part of the game.
 * Warship Gunner 2 after the final boss has one where you have to sink a superweapon.
 * NavalOps: Warship Gunner does this on the second playthrough as well, but there is no mission break after sinking the Druna Skass, the Silfurbor Negla just sails right onto the level and starts shooting.

Western RPG

 * Neo Quest, one of two online Neopets RPGs, features this, with an extra boss added for each difficulty. There are three levels to choose from: Normal, Hard, and InSaNe. On Normal, you'll only fight the standard Final Boss, Jahbal. On Hard, it's Jahbal, immediately followed by Mastermind. The penultimate battle consists of Jahbal, then Mastermind, then Xantan Reborn, a strengthened version of the first boss you fought, Xantan. You get no break between the three, and losing to Mastermind (or anyone, if you're playing on InSaNe) completely erases your save data. Have fun with that.
 * Infinity Blade has the God Kings. After you've played through the castle your first 15 or so times, you can actually buy the Infinity+1 Sword. This actually opens the doors to the four new immortal kings. The first three are really no problem, but the third is a Level 300 (the level cap in the game is 100 for players) robot mech with a man inside it. But you do get a sweet cinematic if you can best this insane challenge.

Misc Games

 * A driving/animal-catching game called Jambo! Safari had the goal was to catch (and presumably tag, not actually poach) wild animals on the African savannah. The last level was an all-or-nothing attempt to capture a saber-toothed tiger... unless you managed to get there in a single credit, in which case your final target was a white lion. The game's Attract Mode seemed to imply that if you somehow attained an even more perfect run, you'd have to catch a Moa.