Ditto Fighter

"I know all her moves. Therefore, I have the upper hand."

- Leela referring to her alternate-dimensional doppelganger.

A staple of Fighting Games, though not by any means uncommon in other genres, this character copies the moveset of the other characters. Generally, the Ditto Fighter comes in three variants:
 * Mokujinner: The moveset is chosen randomly, sometimes per round. If the character is playable, the player may or may not be able to change between movesets.
 * Dittomediate: The Ditto Fighter copies the moves of the opponent they're facing, sometimes copying their appearance if they're lucky.
 * Tsungxpert: The moveset is non-random: the player has full control over what character they copy or the moveset is a predefined combination of moves from already-existing fighters.

In most cases, the moves tend to be less effective since they're built for the original character model's size/height, unless the Ditto Fighter is also the boss of the game.

Named after the Pokémon Ditto, who can transform into its opponents. See also the related Ryu and Ken, where two characters have the same moveset. Similar to, but distinct from Mega Manning, which involves being able to copy one power/skill that your opponent displays and accumulating them as you encounter more of them; whereas the Ditto Fighter copies the whole power or skill set for one round or match and discards it to fashion a whole new skillset upon facing a different opponent.

Action Games

 * The "copycat" dolls from Mendel Palace, with the added bonus of only moving and attacking when you do (except when the alarm sounds).
 * There's a Doppelganger boss in one of the final missions in Devil May Cry 3.
 * Castlevania III: Dracula's Curse also has a Doppelganger boss, as did Castlevania Chronicles and Castlevania: Symphony of the Night.
 * In Castlevania: Dawn of Sorrow, one of the main bosses that you fight can copy your every special move. However, he will always use whatever power you used last, so he is easily beaten by casting some useless spell such as Dracula's Flower Arranging or something, right before proceeding to kick his ass with a giant sword. If you aren't paying attention and don't realize this, he's a lot harder - his default attack is a pain.
 * The Final Boss in the arcade version of Double Dragon II: The Revenge (who is the next-to-final boss in the NES version) is a Lee brother clone who uses the same basic moves, but can also throw energy beams and possess the player's body to drain their energy. If two players are playing, then both players must fight two clones, one for each.
 * Black, the Final Boss of Final Fight 3, has personalized versions of Guy's Tooshi and Haggar's Double Lariat among his move set.

Action-Adventure Games

 * The final confrontation in Zelda II the Adventure of Link is with Link's own shadow, who has all of his strengths and weaknesses.
 * Shadow Link reappears in Ocarina of Time in the Water Temple, and in a few other games. He copies your regular attacks only. Your other weapons (Biggoron's Sword, Megaton Hammer, Din's Fire, etc.) are something only you have. Though he also gets a cheap-ass move where he pins your sword in place by jumping on it.
 * Something unique about this Ditto Fight is that he also copies your health; however many Heart Containers you have is how many hits it takes to kill him.
 * Similarly, in Exile, Sadler is forced to fight his own Shadow before his final battle with The Holy Roman Emperor.
 * Kingdom of Loathing has the Doppelshifter Familiar which will change into a random familiar at the beginning of every round.
 * They also now have a Tiny Costume Wardrobe, which is familiar equipment, and allows the familiar to enter the wardrobe, and come out and act as a different familiar for that adventure. However, it's random.
 * In A Boy and His Blob, one of the eponymous blob's transformations is a doppelganger who copies your moves exactly.
 * And in addition to this, there's an enemy who mirrors the boy's actions.
 * In Lufia: Curse of the Sinistrals, Dekar can equip almost any weapon. Since each character only uses one type of weapon, this essentially means that he can mimic any character's fighting style, except for two moves which are replaced with his own.

Eastern RPGs

 * The Mime class in Final Fantasy V (and Gogo, the designated Mime in Final Fantasy VI) can alter its command menu to include commands from almost any other class in the game, as well as using a Mimic command that copies the last action used in a fight.
 * Mimes in Final Fantasy Tactics mimic the last action performed by a friendly unit, right down to the equipment used in the attack. Difficult to use since their mimicry is automatic and copies everything exactly. For example: if an Archer targets a square that is five spaces forward and two to the right, the Mime will also attack five spaces forward and two to the right using the same weapon.
 * Gau from Final Fantasy VI could copy movesets and even elemental resistances from monsters you had previously encountered, although he's somewhat unique in the fact that he has to be in a specific area of the world in order to do so, but once he learns them, he keeps them.
 * The Duplighosts of Paper Mario transform into your partners in battle. The Duplighost of Paper Mario: The Thousand-Year Door, transforms into Mario partway through the first battle with him. He retains this disguise until you defeat him the second time.
 * Actually, he turns into Mario's shadow. Which you then have to beat up, triggering a cutscene showing Mario and his partners taking the Crystal Star and leaving the shadow lying there. Leaving you wondering why the camera is still focused on the shadow, until you find out that Doopliss has stolen Mario's body and somehow made you beat yourself up. Mario's partners don't realise this, meaning you have to fight them before you can get your body back.
 * Poo from EarthBound has his Mirror skill, which nobody ever uses because you're already stronger than most enemies and you can't copy bosses.
 * The monkey Salsa from the sequel can mimic the target's moves, even a tank firing off a shell.
 * And of course the Trope Namer, Ditto, from Pokémon.
 * Mew can do it too, but you'd have to be up against something really nasty to justify turning a legendary into it. Smeargle too, sorta...
 * Smeargle is definitely an example of Mega Manning.
 * In Black and White it's now possible for a Ditto to have an ability that transforms them automatically instead of needing to waste a turn to do it, making it significantly less of a Joke Character.
 * Rue from Threads of Fate has this ability; you can take the form of a defeated monster and, of course, use it's powers. There's a catch, of course: you can't become boss monsters, and you can only store up to five monster forms at a time, after acquiring a new form, the oldest one will be discarded.

Fighting Games

 * Suffice to say that Namco loves these:
 * Mokujin/Tetsujin, and Combot, from the Tekken series change movesets per round (Mokujin) or per match (Combot). To a lesser degree, "Unknown", the boss from Tekken Tag Tournament, who can change styles within the round but only copies the movesets of small-framed fighters (being a slight female herself, some of the moves used by large fighters such as the Jacks or Kuma/Panda would look ridiculous if used by her) and always starts each fight using the moveset of Jun Kazama.
 * Edge Master and Inferno from Soul Calibur; the latter is notable for being the final boss. This is also a subversion, as Inferno has exclusive special moves.
 * Charade (and Inferno again) from Soul Calibur 2. Necrid used a fixed moveset made of attacks from other characters, complete with an Energy Weapon that changed shape to suit the move in progress.
 * Olcadan from Soul Calibur 3. Somewhat underwhelming considering his cosmetic originality - he's got an owl's head. Though to be fair, it was his punishment for defeating a god.
 * In general, in all of these games, the ditto fighter tends to be inferior to the characters he's copying because he usually uses his own limb length, speed, etc
 * In 3, the custom class job of "swordmaster" allowed them to use every single one of the custom movesets, meaning that you could very well be this in Chronicles of the Sword, where you can change weapons between battle chains and can see the name of the weapon of anyone on the field.
 * In 5,, and  serve as the ditto fighters, with  emulating the male characters' styles,  mimicking the female characters' styles, and  mimicking all styles.
 * Dural from the Virtua Fighter series uses a single moveset taken from a number of characters but Dural's version is usually faster and more damaging than the original move.
 * Metal Sonic from Sonic the Fighters, like Dural in Virtua Fighter, uses a moveset that is an amalgam of the other fighers' moves, plus a few moves all his own, like a devastating Chest Blaster.
 * Shang Tsung from the Mortal Kombat series had the power to shapeshift into any other character at will, via button combos. In the first Mortal Kombat, he was the final boss.
 * Also, in Mortal Kombat Trilogy, the characters Khameleon (female) in the N64 version and Chameleon (male) in the PS version would randomly switch their moves and looks between the female (for Khameleon) or male (for Chameleon) ninjas. In Mortal Kombat Armageddon, both characters still retain a few special moves from their fellow ninjas.
 * In Mortal Kombat 4, the character Meat was essentially a 'skin' over whichever character you chose, acquiring all their moves. The playable boss character Shinnok could also switch between the other characters' moves with ease.
 * Finally, in Mortal Kombat: Deadly Alliance, while they didn't share any special moves with anyone else, Blaze and Mokap stole all three of their fighting styles from the other characters in the game.
 * Shujinko, the protagonist of its immediate sequel, Mortal Kombat: Deception, has specials either reminiscent of or direct copies of moves used by other fighters; this is justified because in most cases those fighters taught him those moves over the course of Konquest mode.
 * In Mortal Kombat vs. DC Universe, Shang Tsung's shapeshifting has been swapped out for a Freaky Friday Flip. However, one of his fatalities has him transforming into his victim for the hell of it as he absorbs their soul.
 * In Naruto, Kakashi is able to mimic the movements of his opponent thanks to the Sharingan. In various games based on the manga, he can imitate to a certain point the fighting style of his opponent. As can Sasuke. This leads to many funny techniques: Sexy Jutsu Kakashi? Inner Sasuke? Yeah.
 * In some of the Clash of Ninja games Kakashi can activate his Sharingan in place of his special move. This changes his counter move such that if he is hit with another players special he will dodge it and then send it right back. Some special moves involving equipment or bloodline traits are not copied and he will simply dodge. But watching him copy Sakura's Inner Sakura beatdown and unleash Inner Kakashi is hilarious.
 * The secret characters Shadow (mimics the last character you beat) and Marionette (mimics the character you're fighting against) from the Darkstalkers series.
 * In Super Smash Bros. Melee's Tournament Mode, to select a fighter randomly, you had to choose... you've guessed it, Ditto. For another example, look at Kirby.
 * There was also originally a plan to make Ditto a Poke Ball Pokemon in Melee, with the ability to turn into the fighter who released it and then fighting alongside the person as a separate fighter. The idea was scrapped when it created lag problems. For example, a battle between four Ice Climbers already would have lag problems, but imagine if each of them got a Ditto at the same time. That would be SIXTEEN bodies on the field all at once.
 * Black, in some versions of Archon, had a Shapeshifter unit that could be used to duplicate itself against White. Unfortunately, there was no way to capitalize on this, as White would have the same advantages as you.
 * Except that, as all pieces have their health modified by the luminosity (color) of the square they're on, the Shapeshifter can trade blows and win on dark squares - and (unlike the other pieces) its wounds disappear at the end of the fight, making aggressive assassination of misplaced Light pieces practical.
 * In Dissidia Final Fantasy Bartz is a self-described Mime who uses an amalgamation of techniques from the other heroes to fight with. These are customized by the player, making him a rather flexible Ditto Fighter.
 * While his HP attacks are identical, his Brave attacks combine two different characters' brave attacks into one. For example, one of his brave attacks is Slidehazzard, a combination of part of Tidus's Slide Impulse, and Cloud's Climhazzard. Or Solid Ascension, a combo of Squall's Solid Barrel and Warrior of Light's Ascension.
 * In the game Jump! Ultimate Stars, in Planet P, mission 1, players 2, 3, & 4 all use whatever koma deck you choose.
 * Ditto in the D.Gray-man planet, mission 2.
 * In the Last Blade series, Akari can use enchanted paper dolls to briefly become her opponent. A cheat, similar to the Darkstalkers cheats described above, allows you to play as one of the dolls, meaning every fight is a mirror match.
 * In Street Fighter III 3rd Strike, Twelve's "X COPY" Super Art allows him to mimic the fighting style of his opponent for a limited time, with the exception of their Super Arts and EX Specials.
 * The Street Fighter EX series has the Cycloid robots, Beta and Gamma, who both use moves from other characters (one specializes in command-based moves, while the other uses charge-based ones).
 * The Final Boss of Street Fighter IV, Seth, uses souped-up versions of many of the other fighters' special movies.
 * The final boss of the original World Heroes, Geegus (whose name is clearly a mistranslation of "Gigas"), takes the form of a different character each combat round, only returning to his true form for his Victory Pose.
 * An upgraded version of him known as Neo Geegus, later appeared in World Heroes 2 as the semi-final boss, which added, but mostly imitates the newly added characters of the game (excluding Neo Geegus and Dio).
 * In Magical Battle Arena, Sakura Kinomoto can use The Mirror to "shapeshift" into a character she's fighting against for a limited time not unlike Shang Tsung.
 * In X-Men vs. Street Fighter, Rogue of the X-Men could get an opponent's special move à la Kirby in Smash Bros. by kissing them. In Marvel vs. Capcom 2 this was changed to a temporary augmentation of power, speed or defense depending on the kissee (To be fair, it has a 56 character roster).
 * MUGEN-based versions of Rogue try to emulate this too, some better than others, but with limitation due to the same problem; the huge and expanding number of possible opponents.
 * Ryu in Marvel vs. Capcom Clash of the Superheroes had a style-switching power that gave him Ken or Akuma's moveset, to compensate for their in-game absence.
 * The fan-made Pokémon Fighting Game TYPE-WILD has an actual Ditto as its final boss.
 * Rugal Bernstein was originally going to copy the moveset of the character you were playing as. Hardware limitations forced the idea to be abandoned. Rugal having Geese's Reppuken and Krauser's Kaiser Wave were pretty much the ashes of this.
 * Guilty Gear Isuka featured Robo-Ky MKII, a version of Robo-Ky that by default, had Robo-Ky's standard movelist from Guilty Gear XX Reload. The player could customize it, replacing many of it's moves, with imitations of other characters' abilities. From GGX to the original GGXX, Robo-Ky itself was a sort of ditto fighter to the real Ky, imitating a number of his moves whilst having a few of its own unique moves only seen in them two games.
 * In the extremely strange fighter 3D Ballz, any character can transform into any other one through special button combinations.
 * Rogue in X-Men: Next Dimension can power-steal, similar to X-Men vs. Street Fighter, but the extra attack she produces can be a variant on one of the character's normal or special moves that they wouldn't possess on their own.
 * Dittomediate applies to the B-button attack of Kirby in Super Smash Bros. series.
 * Mildred Avallone and Parace L'Sia, two boss characters from the Arcana Heart series, are capable of using a mixture of attacks from all of the other Arcana.
 * Double from Skullgirls is an interesting variation. While her normals mostly copy moves of other fighters, they often have different properties. In addition, while she morphs into other characters for her special moves, all of them are unique to her. Word of God states that many of Double's special moves were moves Dummied Out from other fighters.

Platformers

 * Doc Robot of Mega Man 3 used the techniques of all the Robot masters from Mega Man 2.
 * The Final Boss of Mega Man Zero 3 uses all of the attacks that Zero himself was known for in the Mega Man X series. Justified,
 * While the Mega Man games almost invariably center around Mega Manning instead of this, the Mega Man ZX games discard it in favor of Ditto Fighter abilities. In the first ZX game, beating a boss either unlocks a new transformation or upgrades an existing one, and in ZX Advent, beating a boss simply unlocks that boss as a transformation.
 * Many games in the Castlevania series include a boss called Doppelganger which at first glance appears to be an Evil Twin but is really closer to this. The boss is supposedly a demon that has taken the form of the hero to Beat Them At Their Own Game. If they were a true Evil Twin they would have more of a purpose in the plot but once you kill them they are never mentioned again.
 * The only exception is in Lament of Innocence where you fight the doppelganger twice, but it still doesn't serve any purpose to the story aside from another Boss Fight.

Racing Games

 * The hidden characters Petey Piranha and King Boo of Mario Kart: Double Dash can use all of the character-specific special items.
 * In Sonic Rivals, Metal Sonic copies the special move of his current opponent. This is also the only way for both players to have the same one in multiplayer.

Shooters

 * Touhou's Satori Komeiji in Subterranean Animism uses spell cards pulled from your partner's boss appearance in previous games, also making her a pseudo-Nostalgia Boss. Her specific superpower is that she can "read hearts" to somehow absorb the use of innate superpowers, even ones that specifically depend on the species of youkai or specific bloodline to use. ZUN has a habit of not exactly thinking even the general limitations or potential applications, much less exact mechanics, of the superpowers he hands out.
 * It's less copying their powers than copying the danmaku patterns they use. And before she can copy your partner's spell cards, she has to use her Recollection "Terrifying Hypnotism" spell card to take them out of your character's memory. It still doesn't explain how she can turn into mist if your partner is Suika, though, unless that's just an illusion.

Sports Games

 * The Mii in Mario & Sonic at the Olympic Games is normally the Jack of All Stats, but in Winter Olympics, you can make one copy every character, even some bosses, through costumes that they wear.

Puzzle Games

 * In both Meteos and Meteos Wars, you play as one of these during the story mode.

Non-Video Game Examples

 * In his fight against the series' first Big Bad, Kenichi: The Mightiest Disciple does this, mimicking his masters' moves and personalities to throw off Odin, who had been reading his rhythm to counter his attacks.
 * Another example from the same manga: Kisara twice defeats an oponent by copying Miu's moves, because her usual fighting style wasn't enough to penetrate the oponent's defence: once fighting against Freya (because Freya was fighting with a staff), and once during the D of D Tournament (because her oponent Aysha's legs were longer than hers). During the fight with her next tournament oponent she realizes that copying someone else's style is not enough and it's then when she developes her own fighting style.
 * Wrestling example: In late 2008, Charlie Haas has taken to dressing as various WWE stars (past and present) and attempting to mimic their fighting styles. Including Santa Claas (as a Holiday joke).
 * Carlito was the first character Haas imitated.
 * Many of Haas's matches with this gimmick were against John Bradshaw Layfield.
 * Charlie Haas's impersonations got their own Slammy award category. His Beth Phoenix imitation won.
 * Kamen Rider Decade, thanks to his powers of Mega Manning, can transform into any of his nine predecessor Kamen Riders. The Big Bad from the Amazon's World story arc can perform any of said Riders' Finishing Moves, as well.
 * In comic books, this is often dubbed "photographic memory" or "photographic reflexes", and it's a common power for B-list heroes and villains. These characters are always doomed to lose, either because the hero they're stealing the powers/moves from comes up with a new one on the spot, one that drops the mook down before he/she can copy it; or inversely because the hero refuses to fight at all - with no attack to copy, the mook can only rely on his own fighting skills, which of course suck because he's never needed them before. Taskmaster is one of the major examples in Marvel Comics. Tasky is also in Marvel vs. Capcom 3, though in that game he has a pre-defined move set borrowed from various characters including Captain America (comics), Spider-Man, Hawkeye, Black Knight, and others.
 * Also worth mentioning is Kl'rt the Super-Skrull, who has the powers of all of the Fantastic Four. There are several other Super-Skrulls including Criti Noll (with powers borrowed from several Avengers) and Rl'nnd (with powers from several X-Men). Kl'rt is, like Taskmaster, in Marvel vs. Capcom 3 and serves duty as a representative of the Fantastic Four series.
 * DC has Amazo, an android with the powers of the Justice League. In a Literal Genie moment, he was once defeated when Superman disbanded the League, leaving him powerless against a group of now indepentant superheroes.
 * Mirror Go.
 * From Magic: The Gathering, there are several such cards; for example: Clone, Renegade Doppelganger, and Rite of Replication, which can create multiple copies for an additional cost.
 * The Yu-Gi-Oh! anime has Joey using the Copycat card for similar tricks. It doesn't actually work that way in the card game.
 * The Copycat card would not be released until a good half decade or so has passed since it's appearance in the anime and was made to compliment the new game system that has been introduced since then.
 * Ryner's Alpha Stigma does this extremely quicky.
 * The Stellar Spirit Gemini from Fairy Tail has this ability. This logically resulted in a once-off gag in the Edolas arc, where Lucy meets her AU counterpart, and Gemini becomes a third Lucy.
 * Negi's Pactio gave him the ability to copy the artifacts of his own Ministras.
 * Albireo Imma's artifact can turn him into anyone he met.
 * Szayel from Bleach Resurrection's had this as one of his abilities.
 * Both Shirou and Archer from Fate/stay night copy other people's weapons perfectly (well, one magic rank reduced, but that only really matters against Servants like Hercules). Perfectly in this case includes the history of the weapon, including the history of how it was wielded. Meaning Shirou and Archer copy the skill of the original owner. Pray they never copy Assassin's sword, wielded with his reality-bending skill.
 * of Tiger and Bunny eventually develops the ability to copy the powers of the last NEXT she's touched.
 * Duplex of the Whateley Universe has the mutant ability to touch another mutant and gain their powers, although she may not get a full-strength copy off someone.