Swallowing enemies whole. Flying around with a jetpack. Or just jumping high. Video game heroes can have a wide variety of powers; they're fun to play around with, and they'll let you conquer just about any boss battle. You just need to dodge around its attacks and Attack Its Weak Point for massive damage.
But what if those same powers were used against you?
A Mirror Boss, simply put, is a boss in a game whose abilities are the equivalent of the playable character's somehow. This doesn't have to be exact, and it's relative to what the other bosses tend to be like; if most of the game's bosses are gigantic, then just being the same size as the hero counts for a lot, but if everyone in the game is humanoid, a Mirror Boss will have a very similar fighting style.
Depending on how close the boss' abilities are to the hero's, there may have to be some form of "cheating" to insure that the boss is still a challenge. Giving them special immunities to things that would normally destroy the player, some Secret A.I. Moves to separate them from the hero, or just any general application of My Rules Are Not Your Rules to prevent the player from exploiting certain weaknesses.
If this boss isn't an Evil Knockoff of the hero, expect him or her to be a Rival or Evil Counterpart of the hero, and thus an important character in the game.
As you might expect, this is usually a form of Duel Boss.
It's worth pointing out that Dedede actually learned how to do those things by observing Kirby just so that he could use them against him.
Star Wolf in Star Fox 64. Unlike the large bosses encountered elsewhere in the game, Star Wolf comes down to your own level in an attempt to beat you at your own game, flying ultra-advanced fighter craft not unlike your own Arwings. And they seem to do a pretty good job of it, as each Star Wolf member seems to beat his Star Fox counterpart more often than not unless the player is there to save his teammates.
The Blaze palette swapped enemies on the boat level in the first Streets of Rage game. The robotic version of Axel in Streets of Rage 3. Shiva from Streets of Rage 2 and 3, as he possesses similar directional attacks, including a 360 degree defensive maneuver akin to the player's special move button, and a dashing attack.
The Castlevania series has a recurring enemy, Doppelganger, who is a duplicate of whoever the hero of the game is. It first appeared in Castlevania III: Dracula's Curse, where it would switch forms whenever you switched characters. The easiest way to beat him was to switch characters when right next to'em, hit'em once and repeat until he's dead: he'd be too busy changing forms to actually attack you. The Symphony version is interesting in it that it's the only boss that's susceptible to status effects and can thus be made harmless via using several normally useless swords that curse the enemy they hit.
Soleiyu Soleil Belmont from Castlevania II: Belmont's Revenge is the son of the main character, and was kidnapped and brainwashed by Dracula. He is the penultimate boss, wielding a whip like yours, and throwing swords that home in on you.
Richter Belmont in Castlevania: Symphony of the Night counts as well, since he uses a melee weapon and several of the same subweapons as Alucard, and avoids attacks by jumping and sliding.
Hugh Baldwin from Castlevania: Circle of the Moon wields a sword instead of a whip, but he uses your subweapons as well. He also has a variety of special sword techniques which are roughly similar to the DSS enhancements used by your character Nathan Graves.
Maxim from Castlevania: Harmony of Dissonance is a bit less similar, since he uses a katana and a giant shuriken instead of your whip and subweapons, but overall he's close enough to count.
Dmitrii Blinov from Castlevania: Chronicles of Sorrow is a much closer match, since he has the power to duplicate any attack you use against him. And if that doesn't work, he'll just stab you with a knife. Since he'll stick to what he copies and then spams it liberally afterwards, he can either be That One Boss or a Breather Boss: for example, using any high-powered, MP-expensive, hard-to-avoid attack on him isn't too smart, as he has no MP to worry about, but since he only uses the souls at their level 1 strength, some of them are hilariously ineffective. The most notable of them is probably the Cave Troll soul, which causes the user to attack with an elongated tongue: however, since the level 1 version of it only has a range of a few pixels, he'll spend most of his time hopping around harmlessly sticking out his tongue at you.
If you never use a soul attack on him (for example, because you never caught on to the mimicry thing), he sticks exclusively to Malachi's soul — which makes the fight quite a bit harder, since that attack is very hard to dodge.
Some souls are of course much funnier when you use them in practice. Yorick is one of the most hilarious primarily because Dmitri can't slide kick. So you can throw that soul at him (hitting him with it while he has Malachi active is the hard part). Once you got him though, he now has an attack that is puny, hard to hit with, and slow as hell. Have fun beating him up. And in this case, since Yorick's damage goes up to the triple digits if you kick it, you can kill him in a few hits while he is busy chucking skulls at you. However, giving him stuff like Amalaric Sniper or Abaddon is just asking for it.
Of course he WILL activate any secondary soul you have active if you activate one.
Portrait of Ruin also has a Mirror Boss in the form of the Doppelganger at the bottom of the Nest of Evil Bonus Dungeon
Albus fills this role in Castlevania: Order of Ecclesia. His guns are functionally similar to Shanoa's magic attacks, and he even has his own Glyph attack. On higher difficulty levels, he gains extra attacks which mirror Shanoa's elemental Glyphs exactly.
Julius Belmont from Castlevania: Chronicles of Sorrow. He doesn't fight exactly like the player character, but he is human, and he fights exactly like a Belmont (duh), up to and including the classic subweapons.
Metal Sonic in Sonic the Hedgehog CD, as well as many other Sonic robots built by Robotnik which may or may not be the same one remodeled. The first one appeared in Sonic the Hedgehog 2, and was also the first boss in the series who wasn't Robotnik.
Also see Sonic Adventure 2. The whole game was replete with mirror bosses, having each of the characters fight their alternates on the other team. You basically have to fight each mirror boss twice, since they are the exact same regardless of which team you are playing on and both teams have to be completed in order to get the Golden Ending.
Knuckles in Sonic 3 & Knuckles, if you're not playing as him. He's ridiculously easy to beat, but Hidden Palace Zone is a Breather Level anyway. He is pretty much the same Knuckles you can play as, only with some HP instead of rings, a punch attack, and the ability to block by ducking. He even takes collision damage, though trying to walk into him will just get you punched. But you can stand in front of him and get Tails to walk into him from behind if playing as Sonic and Tails. Tails takes damage too, but he's invincible (in 2P mode). If Knuckles drops from a glide on your head, only he will take collision damage.
The fake Knuckles in Sonic Advance works the same way... until you hit it four times, at which point its skin explodes to reveal it as a robot capable of firing huge frickin' missiles.
In Sonic Rush, Sonic fights Blaze, although some of the moves used by the AI character aren't available for the player, even when playing as that character. The 2006 game also has Silver fight Sonic and Shadow. And the various fights against Sonic/Knuckles/Gamma (depending on who you're playing as) in the story modes of the first Sonic Adventure.
Half of the bosses in both Sonic Rivals games are battles with another playable character. Doubly so as every character plays exactly alike.
Also, in Sonic Generations, Shadow has all of the moves that Modern Sonic has... including Boost.
In Sonic Heroes the bosses of the City and Jungle areas are other Moveset Clone playable characters as well, though they vary depending on who you're playing as (Team Sonic vs. Team Rose/Team Dark vs. Team Chaotix in the former and Team Sonic vs. Team Dark/Team Rose vs. Team Chaotix in the latter).
The Bonus Boss of the GBA remake of The Legend of Zelda: A Link to the Past is four copies of Link in different colored tunics as they are portrayed from the Four Swords game. Each Link uses different abilities that the player can use, such as the Hurricane Spin, using the Magic Cape to become invisible, and the ability to shoot sword beams.
This happens a total of three times in Persona 2. In the first chapter, dubbed Innocent Sin, you fight doppelgangers (or "shadow sides") individually in the Zodiac Temples. One of them, Yukino, is encountered in an earlier dungeon and is optional; in fact, the creation of Yukino's doppelganger hinges on the hero picking the wrong dialog tree at the dungeon's entrance. (Even if the party manages to defeat her, the fake is still victorious, driving the real Yukino to insanity.) In the sequel, Eternal Punshment, the party must fight liquid metal clones of IS's main characters, and later, a straightforward boss rush against doppelgangers of themselves.
Axle Gear from Rocket Knight Adventures, a member of the Black Knights who oppose the Rocket Knights which Sparkster is a member of. Like Sparkster, Axle Gear uses a rocket pack and a sword to battle. He also has the honor of being the only enemy to appear in all three games in the series (and That One Boss in all three of them).
Nelo Angelo from Devil May Cry, a dark knight with the same swordfighting style as Dante, except that he hurls fireballs instead of using guns. He is also treated as a Worthy Opponent by Dante, and turns out to be his twin brother Vergil.
Bolverk from Devil May Cry 2 is often described as that game's equivalent of Nelo Angelo. He also has a connection to Dante (his father Sparda killed Bolverk's comrades, who were reincarnated as wolves) but it doesn't really come up in the plot.
Dante himself fills this role in Devil May Cry 4 when he goes up against Nero. Angelo Credo counts as well.
Another Joe from Viewtiful Joe is portrayed as one of these, though he actually relies on the Doppelgänger Attack while warping around. A straighter example is the final boss, Captain Blue, who has VFX powers like Joe and can speed himself up with them, as well as having a similar moveset to Joe overall. Even moreso when you reach this boss as the final unlockable character, Captain Blue, at which point it's exactly identical... minus the random lightning bolts, of course.
Ninetails from Ōkami. A canine with godlike magical power, who wields a giant sword hovering over her back, and can even interrupt Ammy's Celestial Brush with her own. The second stage of the fight with Oki has him transform into a wolf and wear his sword in the same way Amaterasu wears glaives.
The mirroriness gets cranked Up to Eleven in the sequel, Ōkamiden. The final boss is an evil version of Chibiterasu, and literally comes out of a mirror. He has his own brush, like Ninetails, but the brush vs brush mechanics have been fine-tuned to the point where there is no difference in your abilities bar no matter how many secret brush techniques you picked up. Drawing a technique? He can cancel out with a line. He's drawing a technique? Cancel it with your own line! He even has an evil version of Sunrise that covers the arena in pitch-black darkness.
Azel from God Hand, who possesses the other God Hand and uses the same attacks and Roulette moves that Gene does. Also, the 51st battle in the fighting ring is Double God Hand Gene.
While has lots of Evil Counterpart characters, but few of them fall under this. One that does is The Boss from Metal Gear Solid 3: Snake Eater. In that game, you basically have 3 specialties: guns, CQC, and camouflage. The Boss carries the Patriot machine gun, is the one who taught you CQC, and wears a white jumpsuit which provides excellent camouflage in the field of flowers where you fight.
Liquid Ocelot from Metal Gear Solid 4 engages the player in a close combat based fight at the end.
A very interesting example in Metal Gear Acid 2 - Venusbreaks the fourth wall to announce that she's going to use Snake's deck, even drawing the cards in the exact same order that he does. Since there's a lot of flexibility with the card-based battle system, though, it's very unlikely that she'll act anything like Snake at all once in combat - for instance, a good way of fooling her is by setting up a deck with a few strong equippable gun cards and lots of weaker guns to use as ammunition, which will often cause her to equip the weak ones and load them with the strong ones. The version of her that appears in the Boss Rush also uses whatever deck Snake has.
Wario from Super Mario Land 2: 6 Golden Coins is basically a giant evil Mario. He starts out trying to jump on Mario's head, then uses a black carrot to copy Mario's rabbit form, then finally copies Mario's fireball power with a black fire flower.
Ness's Nightmare from EarthBound possesses all the skills that Ness has. To make it even more apparent, this is also a Duel Boss.
In MOTHER 3, the Masked Man fights in a similar style to Lucas and his party. He hits hard with his weapon, has the ability to destroy your shields like you can with the Shield Snatcher, uses a lightning attack that is similar to PK Thunder, and also possesses PK Love Alpha, Beta, Gamma, and Omega, which is the same powerful technique Lucas uses. The reason the Masked Man can use the powerful PK Love attack is due to him being Claus, brother of Lucas.
In Touhou Project 9.5, Shoot the Bullet, this is Eiki Shiki's last spellcard, "Cleansed Crystal Judgment": a magic mirror that produces a clone of the protagonist that uses her attacks.
The reflection fights like Aya did in the previous game, while she's using completely different mechanics here. The Aya/Hatate fights in Double Spoiler are much closer to the trope, putting you up against a boss that uses photography, although the game is inherently asymmetric.
In the final stage of Gungrave, Grave's first battle in the level is a boss encounter with his former apprentice, Bunji Kugashira. While he doesn't look like his mentor or have a coffin-like weapon, he too dual-wields a pair of pistols and regenerates his health the way Grave regenerates his shield. Bunji's also capable of using his own unique Graveyard Special, which is the same boss fatality move that Grave uses, except Bunji can use his any time he's close to you. His battle even starts with him sliding at Grave, trying to catch him and initiate the move.
Allen O'Neil from the Metal Slug series. Nearly every other boss is some sort of exotic military vehicle, but Allen is just a man with a gun, grenades, a knife, and a whole lot of muscles.
Gargoyle's Quest II had a literal Mirror Boss, a magic mirror who could transform into a copy of your character. There was a trick to beating it: any damage you inflict while it's copying you is reflected back on you, so you can only attack it while it's in its natural mirror form.
Asch of Tales of the Abyss is this to Luke, with very good reason — Luke is his clone. Indeed, in Luke's clashes with him (which are, of course, Duel Boss Fights), he has most of the same skills that Luke does — the only major difference in ability is the fact that Asch can cast spells and his Mystic Arte is different, though functionally similar.
Most of the other Six God Generals count as well, though to what extent varies from general to general.
In the second half of Tales of Legendia, the majority of the non-monster bosses are shadow versions of your party members who can use all of their respective artes, but have the added benefits of flinch resistance, and in the case of the magic users, quick or instant casting on their spells.
The bonus boss of Tales of Xillia copies the fighting styles of your party members, first imitating Alvin, then duplicating himself and imitating Leia and Rowen, then duplicating himself once more to imitate Jude, Milla, and Elise.
Played completely straight in Tales of Xillia 2 with Victor, who's an Alternate Self of Ludger and has access to every trick in his arsenal (Including ones you might not have learned yet). You also fight shadow versions of your party members in the bonus dungeon, who despite facing you solo are extremely threatening due to their drastically increased stats.
Near the end of the first Tomb Raider, Lara meets a copy of herself which does exactly what she does. Shooting it only results in Lara getting injured. You have to lure it into a deathtrap to proceed.
In the Flash game Ginormo Sword, the Temple of the Moon contains a Bonus Boss called Doppelgänger who looks identical to you and has a sword exactly as big as yours. And, as the game's name implies, that's pretty freaking big. Unless, of course, you have your sword reforged to its minimum size before fighting him...
In the Sega Genesis version of ESWAT, the final boss is a man in a red version of your Powered Armor, with several upgrades such as the ability to fire charged shots without charging.
Green in Gunstar Heroes, a former ally of Red and Blue brainwashed to serve the Empire, is a Mirror Boss in the final chapter. His Boss Subtitles list his attacks as "The Gunstars' Actions", which is appropriate, since he can jump, slide, and throw just like you can. But instead of using a gun, he uses throwing stars. This is not true of the remake/sequel, Gunstar Super Heroes, where Green just reuses the Seven Force he used earlier.
Zohar from Silhouette Mirage. Like Shyna, Zohar can switch between the Silhouette and Mirage attributes — and while Shyna's attribute depends on which way she faces, Zohar can change at will. Plus, Zohar's move arsenal contains several attacks which are counterparts to Shyna's — namely, the homing shot and sword attack.
Penta from Radiant Silvergun is a copy of your Airborne Aircraft Carrier base, Tetra. It attacks with two copies of the Silvergun which use all the same weapons that you can use. I hope you've memorized yourself.
Tageri from Ikaruga, a boss who is capable of instantly switching between the white and black attributes just like your ship can, and intermittently using your homing laser superweapon, which you can only survive by absorbing it with the matching attribute. Of course, you're still a small fighter plane, and it's a giant sphere shooting waves of danmaku at you, but it sort of works.
Brad from Sin and Punishment, who wields a gun/sword weapon exactly like yours. He's first fought in a shootout where you have to dodge his aiming cursor to keep him from shooting you; once that's done, he closes in for a sword duel.
Samantha from Stretch Panic is set up to be an Evil Counterpart to Linda even in her backstory: they were born less than a year apart, and Samantha's transformation revolves around an object which is important to her, a toy fish she was given by her mother. This toy fish is connected to her by a prehensile chain and acts like an extra limb, being used to grab and throw objects much like Linda's scarf hand.
The final battle of Ultima IV: Quest of the Avatar is against clones of all 8 recruitable party members. Note that there is one party member of each class, and you can recruit all of them except the one who shares your class, so the clones usually end up having the exact same party makup as you.
A similar situation occurs in the final battle of Rings Of Power, whereas your evil rival has gathered a party of adventurers with the exact same class composition as your own to fight you.
The Bomberman games have a trend of including a Quirky Miniboss Squad of evil bombers as bosses. This trend started with Super Bomberman 2 and its Five Bad Bombers, who had both unique bombs and Humongous Mecha — including, notably, Brain Bomber's giant Bomberman mecha which could also lay bombs.
Pulseman featured as the boss of Stage 5 a dark Pulseman who attacked using a similar 'Voltecker' dash as Pulseman's own (e.g. this video).
Bass, introduced in Mega Man 7. An evil robot created by Dr. Wily to be Mega Man's equivalent in every way, he even has a robot dog, Treble, that he can combine with much like Mega Man can combine with Rush.
Much earlier than him is Proto Man in Mega Man 3, under his guise of Break Man.
In Operate: Shooting Star, Rockman.EXE and Ryuusei no Rockman end up fighting due to a misunderstanding. Ryuusei uses a similar fighting style to EXE with a few negligible differences.
The dark versions of the navis in Mega Man Battle Network 4 and 5 all use the battle chips and program advances that you've been using the most frequently in addition to their own attacks. This can end up making them very difficult if you favor the use of unavoidable attacks, and was particularly nasty in 4, where they put you up against one of them early enough in the story that they could One-Hit Kill you with a program advance if you had used one prior to the fight.
Preceded in the original Mega Man 1 by the second fortress boss, a Mega Man clone who had all of the original's weapons.
The Mega Man clone makes a reappearance in Rockman 4 Minus Infinity. This time he is monochrome. After beating him once, he steals 4 of Mega Man's weapons with Dr. Wily's Stealing System and gains some color. Fortunately, he does not know how to use the weapons well.
Kojiro in Brave Fencer Musashi, a child swordsmanboy summoned by Princess Fillet using the same Hero Summon spell that called Musashi... but instead of rescuing her, he decides to kidnap her to goad Musashi into a duel. Also, the final boss, Dark Lumina fused with Kojiro, uses elemental attacks from the same five elements as Musashi's scrolls as well as a sword combo.
President Gandrake from Musashi: Samurai Legend actually transforms into a copy of Musashi after stealing the five elemental swords for his boss fight.
Sabata from Boktai. While Django wields the Gun Del Sol, a weapon which stores and fires beams of sunlight, Sabata uses the Gun Del Hell, which uses the power of darkness to achieve the same effect.
Anubis in Zone of the Enders: The 2nd Runner. It was built as part of the same project as Jehuty, and not only are they the only two Orbital Frames in existence that can use Zero Shift and control Aumaan, but their normal beam attacks are parallel as well.
In the original Zone of the Enders, Viola and her frame Neith are a Mirror Boss, mainly because all the other bosses are absolutely humongous even by Humongous Mecha standards.
In SaGa Frontier, the entire purpose of Blue's quest is to prepare for a Wizard Duel with his brother Rouge. When the duel finally happens, you find out that Rouge has mastered the opposite of every school of magic that Blue learned (except for Realm magic, which they both start with).
Red's quest has a Recurring Boss named Metal Black, a robot warrior who remodels himself after every defeat. His final form is modeled after Red's superhero identity, Alkaiser; he even has a copy of Red's finishing move, Dark Phoenix.
The Guy from I Wanna Be the Guy looks mainly like a larger version of The Kid, right down to the blue jumpsuit and red cape. And the gun.
One mission in Naruto Shippuden: Clash of Ninja Revolution 3's story mode has Guy fighting himself. The CPU-controlled character copies the exact same moves you do. However, its chakra gauge fills up slightly slower than yours. So not only can you pull off your own special sooner than the computer, but you can even have the computer waste its own.
The Handsome Men from Killer7 are a team of rival assassins who battle the Smith Syndicate in a Duel Boss sequence. Not only do they have one member for each of your 8 characters, but they all copy the weapons those characters use... and every single motion and shot you make, turning every battle into a war of attrition which you are destined to either win or lose. If you pay attention to this being a Mirror Boss along with the cutscene afterwards, this is ultimately Foreshadowing to Harman's status as a Decoy Protagonist to Garcian, as Handsome Red is to Handsome Pink.
In Oni, after Konoko learns her true identity, she has a trippy dream sequence that culminates in her fighting a hostile dream version of herself. The dream Konoko is faster than most enemies and has the same move set as the player, but doesn't use the most powerful specials, so she's not as tough to beat as she could be.
Legacy of Kain: Defiance closes its third act with a Duel Boss fight, pitting the two player characters against one another, first with Kain against Raziel, and then vice versa.
Interestingly subverted in Baldur's Gate: Tales of the Sword Coast, where you face a Demonknight Death Knight and have the option of activating its Mirror of Reflection (which, it is initially implied, might be used against you). Instead of conjuring a Mirror Boss, it instead conjures up weird distortions that attack everyone, as it's broken.
Played with in Baldur's Gate II, where your initial boss fight with Irenicus has him cast a "Summon Clones" spell which doubles your party members as hostiles, only without equipment or spells (so — harmless, really).
Also subverted near the end of Baldur's Gate II, where a random encounter has initially friendly NPCs turning into doubles of your party and attacking if you say the wrong thing — but gives them none of your party's powers, instead making them into a moderately challenging fight at best.
Kojack, the Access Hangar boss in MadWorld, looks a lot like Jack and fights identically to him on a motorcycle. The commentators, of course, have a field day with this — "Jack must feel like he's kicking his own ass!" He's hardly a threat, though.
Less notable but still present is the final boss: The Black Baron, who's on much more equal terms with Jack than most of the other bosses, edging on Fearful Symmetry in their power struggle. They'd be even more similar if Jack's moveset was more like how it is in Anarchy Reigns, such as the spinning kick dive and Rampage Mode.
Kingdom Hearts: 358/2 Days has Xion, who not only fights a lot like Sora from the first game, but also has several of his special attacks, including Sonic Blade, Ragnarok, and Ars Arcanum. Which makes sense, considering what she it is. Not to mention that in its Final Form, it will use Sora's Trinity Limit on you.
Terra's final boss in Kingdom Hearts: Birth by Sleep exclusively uses Terra's own moves against him. His best moves, like Quake and Meteor, Chaos Blade, and the like, and his two best Shotlocks: Dark Salvo and Ultima Cannon. He can even go into Command Styles that Terra is able to use — specifically, Dark Impulse. He can even do things that normally only the player characters can do, like dash, block, counterattack, and [heal himself with Cure spells (he even chuckles when he whips that one out). This is all handily explained by the fact that Terra's final boss is Terra himself. Specifically, it's Master Xehanort after having taken over Terra's body. You play as Terra's cast-off armor, which has risen up to fight under the influence of Terra's memories.
In Kingdom Hearts 3D [Dream Drop Distance], the Armored Ventus Nightmare fights just like its playable namesake from the aforementioned game, right down to finishing the match with a Shotlock, albeit mixing darkness into many of its attacks and having a few new ones of its own. It even uses Payback Raid as a counterattack whenever you knock it back and is the only boss to have such an ability.
Implemented with in-universe justification in .hack//G.U.: The Doppelgangers are designed to be a copy of the player that appears if they hang around too long in a field-type area. The thing is that they are always 8 levels higher than you are (but not above the level cap of the game; 50 in the first game, 100 in the second, and 150 in the third), always has +50% speed, constant HP/MP regen, damage reduction, healing spell, has weapon effects that mirror yours if your weapon is fully customized, and can change weapons at will (mirroring what you use). The difficulty spike reaches to Nintendo Hard levels for unprepared players in Volume 3, although the rewards (provided the player played the two volumes before it) are phenomenal.
In Secret of Mana your quest to find Sage Yoch culminates in the three heroes fighting shadowy twins of themselves that use the weapons when they were first encountered in the story.
In the Metroid franchise, you face off against evil Samus duplicates several times. However, the only one of them that fully represents a Mirror Boss is SA-X. Dark Samus may look like Samus and use the Morph Ball, but she moves very quickly and flies. Even Gandrayda-Samus takes liberties with Samus's abilities. SA-X is confined to things that Samus, post-Super Metroid, could actually do, with the sole exception being the ability to perform the Screw Attack with a completely horizontal trajectory.
The Elder Scrolls IV: Oblivion expansion Shivering Isles has you fight a dark shadow of yourself at one point. As Oblivion uses a character creation system with stats for specific abilites, this shadow is literally your own character, copied and coloured pitch black, with your exact stats and level, right down to the equipment it carries. Its status as a That One Boss depends on how much your own character kicks ass, as the computer has all your weapons and abilities without the need to press buttons to switch between them.
One strategy for easily defeating him is to change your default weapons and armor to something very weak, then when you finally get in the fight with him, change back to your better armor and sword and slaughter him before he can do the same.
Quest for Glory III has a literal (and particularly unpleasant) Mirror Boss fight near the end of the game. The hero and four of his friends arrive in a room with five mirrors, each character walks up to a mirror, and then the reflections mutate into demonic versions of themselves and attack. Hitting your own reflection causes you to take damage, on top of the damage he's already doing to you. There's no way to win on your own... you just have to try not to die until another buddy shows up and stabs your reflection in the back.
In The World Ends with You, certain varieties of Fox Noise can pull this trick on you. When they have enough tails, they can transform into masked copies of Neku and attack with versions of your own Psychs. One of them is an optional boss, the other is a non-boss enemy.
Kariya and Uzuki are a better example. The pair has a light puck, are a pair (sharing the game's two screen combat), and attack with a few common Psychs.
World of Warcraft has 2 bosses where one must face clones of your current party. One is relatively hard, as the clones have ablities and attack patterns based on the clonee's class and spec (IE cones of healers will heal) and each player must fight them off alone. Should you defeat them all, you'll join another party member who is still fighting them until all 5 groups are cleared and the actual boss fight continues. Notably, your own clone set will not have a clone of you, though everyone else will have one of you. In the other fight, they are relatively weak and just act as support for a simple boss.
There is also one quest where you fight against your inner turmoil which is a basically a clone of yourself, though the character only uses melee attacks despite the fact you may be a magic user character, and lacks any of your abilities and strength, making it a easy fight.
Not quite a mirror match, but much more formidable than the above examples, is the Faction Champions encounter in the Trial of the Crusader raid, which pits you against a group of bosses that mimic the abilities of player characters (in a simulation of a PvP Arena match). While they lack the benefit of human intellect and are fewer in number than your raid group, they are statistically far superior to a PC of the same class and spec and have a habit of dogpiling one member of your team.
There's also Nefarian (the old one), who while not exactly mirroring your abilities, does mirror some icconic class abilities: Druids are forced into cat form, Rogues are teleported in front of him and stunned there, he Death Grips people if there's a Death Knight around, etc.
And Hex Lord Malacrass, a Zul'Aman boss that steals some of your (most annoying) abilities.
Issue 17 of City of Heroes introduced Doppelgangers, enemies who copy the player's look and powers. However, they are not exact duplicates — most notably, they only copy the powerset, but not the particular powers a player has picked. Every story arc introduced in Issue 17 contains, in some way, one of those. One mission gives you the option to fight eight copies of yourself at once. The badge for achieving that feat is particularly amusing.
Army of Me: You don't understand the math behind it, but you're pretty sure you're equal to or greater than eight of yourself.
The Elites in Hero Core. Significant in that it isn't just a random Evil Knockoff; they foreshadow that Flip Hero is also an Elite that once served in Tetron's army.
The "Shadow Boss" at the end of the NES version of Double Dragon is none other than Billy's twin brother Jimmy, who has all the same moves as the player and more health. This is actually a carryover from the arcade version, in which both players were forced to fight each other at the end (Jimmy was originally Player 2 in the arcade version, but became the Final Boss in the NES version due to the omission of the 2-Player mode).
Jeff, the Mission 2 boss in the arcade version, also fits this trope, being a Lee brother Head Swap with all the same moves.
In the arcade version of Double Dragon II: The Revenge, the final boss is a Lee brother clone who has all the same moves, plus an energy beam attack and the ability to possess the player's body and drain his health. If both Lee brothers are present, then there will be a second clone as well. The clones appear in the NES version as well, where they are the last enemies before the new final boss.
In a rare movie example, Scott Pilgrim vs. The World, the last enemy Scott Pilgrim has to face is Nega-Scott, a shadowy version of himself... but instead they talk things out and decide they have a lot of things in common, and head their separate ways.
In the comic, Nega-Scott is "defeated" when Scott accepts him and admits that he's partly to blame for things going wrong with his life, since fighting him just means he's fighting himself and refusing to learn anything.
The game plays this trope straight by including Nega-Scott as a boss, though you don't have to play as Scott to face him. He ultimately subverts it by having attacks that the real Scott can never pull off.
In Purple, all but one of the mini-bosses you encounter on the map wield the exact same weapons you do. The final boss also uses these weapons, but they're bigger and some have extra effects.
Super Paper Mario has the boss of World 4, Mr. L. He jumps and moves around like the player, and he can even use items to heal himself.
The boss of the Flopside Pit of 100 Trials, Shadoo, transforms into Dark versions of the four playable characters that use their special abilities to attack (except for Dark Mario, who uses Cudge), each with 100 HP and 10 Attack (20 for Dark Bowser, mirroring Bowser's Attack being double Mario, Peach and Luigi's). His Dark Luigi form even resembles Mr. L.
Shadow Mario from Super Mario Sunshine uses many of Mario's jumping abilities to escape him whenever he shows up to kidnap Princess Peach. His Magic Paintbrush matches F.L.U.D.D. insofar as that they were both made by Professor E. Gadd. He's actually Bowser Jr.
Jade Empire uses this quite successfully. While many boss encounters deal with 20 foot tall Golems, spirits gone bad, or groups of Elite Mooks, the final boss encounter is a one-on-one fight against someone who uses abilities very similar to your own. Which makes sense; he taught them to you. This works as a strong display of the strategic depth that the game creates: that the final boss can be a character just like yourself, while still giving an entertaining, difficult-but-fair final confrontation. No weak points to aim at, nothing like that. The final boss blocks, attacks, dodges, heals, etc., all exactly like your character can. You must display mastery of your combat forms to stand a chance.
At the end of Extermination, after defeating its giant monster form, the Alien Lifeform transforms into a copy of your character; basically a soldier with an assault rifle.
Happens near the end of Drakensang 2. The clones sports the same weapon you're using, so if you disarm your character right before the cutscene where the clones are created, the clones are unarmed and helpless.
Mr. X from Kung Fu Master, who can attack with the same punch and kick animations as Thomas, in addition to his advantage of knowing how to block. This is more noticeable in the NES port, where Mr. X is a head-swapped black Palette Swap of Thomas.
The third boss in Crash Bandicoot 2 N Tranced is Fake Crash, who mimics the player's movements. Like the Tomb Raider example, the only way to beat him is to move him so he stands where you shouldn't. If you collide into him, you'll die and he'll produce a cheering animation.
Jin from Panzer Bandit uses an exact duplicate of Kou's moveset, with the exception of the visuals of his second Hyper attack (though move-wise it's the same effect). Tsubai serves as a mirror to Ein as well, mostly in techniques having the same function rather than being mirror-sprited like Jin's.
Tenchu 3: Wrath Of Heaven introduces Hyakubake, a Master of Disguise who takes on either Rikimaru or Ayame's form in the opposite's Story Mode, making use of their techniques and even a few of the player's items (like the Blowgun). This trend of pitting one of the two (or three) playable characters against the other is used in other games (Fatal Shadows and Time of the Assassins, for example), though in most of those cases it's the actual character instead of a disguised enemy.
To a lesser extent, Lord Gwyn, the final boss. He operates very differently than the player character, but he is a swordsman of roughly the same size as the PC, whereas most of the game's bosses are giant monstrosities.
In Death Smiles, Sakura is the boss of the Swamp, which means that if you're playing as her in Mega Black Label mode, you fight a mirror image of her.
Bayonetta's rival, Jeanne. She'll gain abilities as Bayonetta does during the story, getting harder and harder but never outright overpowering Bayonetta and her abilities.
Angel Slayer, however, has Bayonetta herself as the ultimate Mirror Match, who can use the exact same techniques and weapons she can, just while dealing much higher damage.
Prince Vorkken uses the Unify Morph, which functions much the same as the Wonderful Ones' Unite Morph. Vorkken, however, uses a bit of My Rules Are Not Your Rules (such as being capable of blocking any attack with Unify Guts) to increase the challenge. Like Jeanne in Bayonetta, he will also gain abilities as the game goes on, and will never use an ability that the player has no access to yet (excluding Vorkken's Boomerang and Chewgi's Naginata, their own signature morphs that they will always have access to). In the case of their special Unite Morphs where they transform into GEATHJERK enemies, they won't transform into something the group hasn't encountered yet.
Wonder-Jergingha will use the pieces of the shattered platforms and machinery around him to mirror the Unite Morphs of the team. He will only use the main sevennote Hand, Sword, Gun, Whip, Hammer, Claw, and Bomb, though.
The climactic battle of Level 4 in Descent 3 is a duel with one of Dravis' Black Pyros.
The final boss fight of Asura's Wrath is Gohma Vlitra's Core, which looks like a bigger and meaner, but still nearly identical version of Berserker Asura, Giant Arms and all.
The final boss of the DLC uses quick time events, even with similar on-screen inputs.
In Guild WarsProphecies, the final test for Ascension is defeating an enemy with the exact skills your character has equipped.
The Traitor's Keep DLC in Fable IIIends with a fight against a doppelganger of your Hero. The copy utilizes all your abilities while talking you down and telling you why you need to die.note Though if you've succeeded in playing as a good Hero up to that point, said speech (which essentially remains unchanged) starts to sound more like the copy's grasping at straws trying to find legitimate reasons to kill you.
Inverted with the fight with Arikan in Copy Kitty. The player is mirroring him. Even better, when Arikan decides to get serious and Turns Red, the player copies that too, and gets the same power enhancement.
In La-Mulana, the Mini-Boss Shu (or Chi You in the remake) somehow can use all the player's sub-weapons.
A slight variation in Star Trek The25th Anniversary, where the final boss is a copy of the Enterprise but with plasma cannons and two escorts that show up about a minute into the fight.
In Gravity Rush, Raven serves as this. She even counters Kat's finishing move by mimicking it.
In the Citadel DLC pack of Mass Effect 3, the primary antagonist is an evil clone ofShepard. They originally appear in a different set of armor, but when you actually fight them, they've stolen some of Shepard's N7 gear and inverted the default colors to complete the look. And whatever class you're playing as, they match. "That's creepy."
The 4 Faeries in NeoQuest II. The Earth Faerie mirrors Rohane (has Critical Hits and Stunning Strikes), the Fire Faerie mirrors Mipsy (Direct Damage, Group Direct Damage), the Dark Faerie mirrors Talinia (sort of; it's the one that inflicts status effects, even if Velm gets some of them on your team) and the Water Faerie mirrors Velm (Healing, Group Healing).
Dishonored has Daud, who like Corvo has powers granted by The Outsider and uses Sword and Gun in combat. Of course, the player doesn't have to directly fight him and can simply sneak up on him or sneak by him if they wish.
Kamui has the bosses of Stage 4, a squad of Kamui fighters just like your ship. Just like the ship you pilot, they can use standard shots, lock-on shots, and a beam attack (although heavily modified).
Strider Hien in Strider 2 has all of Hiryu's techniques and movement, jumping and climbing included. The only difference is that he fights with ranged attacks instead of Hiryu's close-and-personal approach.
Among all the giant bio-organic monsters in Run Saber there's Kurt, a defective Run Saber who fights with similar attacks to the protagonists, and even has his own Special Attack.
Raksasha, the cyborg samurai from Hagane, is the only boss without a One-Winged Angel true form to fight Hagane on even grounds as a normal-sized warrior.
Moon Snail, the final boss of Snailiad. Aside from changing his own gravity, he uses Devastator-style boomerangs and dark-colored waves in his first form. As Giga-Snail, he uses bigger Rainbow Waves, as well as using the Devastator-peashooter bullets. He even uses the idle animation as an attack; the Z's fly off in your general direction.
The final boss of Pac-Man World uses one of Pac-Man's moves for each of its phases.
Final Fantasy XIV has a few bosses that are essentially the classes players use (Thamatuge, Archer, Lancer, etc) and can use the same skills as the player can. However, some of the boss characters will use skills that are unique to them and can't be used by the players.
RuneScape has you face off against the appropriately-titled 'Me' during the quest Lunar Diplomacy.
Me: Stop hitting yourself!
Shovel Knight has Black Knight, who looks and fights similar to the titular Shovel Knight, though he gains more unique moves each time you fight him.
Assassin's Creed: Rogue has a former Assassin turned Templar hunting down current Assassins, who are able to utilize some of the same methods as the prior games' playable Assassins such as taking the player by surprise from the air and hiding in foliage, although the Templar in turn has gameplay mechanics to counter those.