Our hero is in a duel with a crafty Shapeshifter villain. It looks like the shapeshifter is going to lose, until he busts out the most underhanded trick of all — suddenly impersonating one of the hero's loved ones or True Companions, trying to cause him to lose his will to fight.
Usually, the hero ends up struggling to find the willpower to continue beating up someone who looks just like his mom/girlfriend/little sister. Bonus points if the form the shape shifter takes on is that of a dead little sister, for extra guilt.
Also covers clones and other doppelgangers who suddenly reveal that they happen to resemble the hero's mom/girlfriend/dead little sister/Dead Pet/whatever.
If the protagonist is an Anti-Hero, there's the possibility that they won't care at all about what face they are kicking in as long as they know whose face it actually is - the bad guy's.
There's also an increasingly common subversion: because of personal issues between the hero and the character the shape shifter takes the form of, the hero actually becomes more willing to attack. Also, all the shape shifter may do is succeed in pushing the Relative Button.
Also see Shapeshifter Swan Song. Contrast Shapeshifting Seducer.
Envy of Fullmetal Alchemist positively loves this. In a pivotal moment, it uses this to kill Hughes by transforming into a replica of the wife he adores, which makes poor old Hughes hesitate just long enough to get shot. And given Envy's regenerative powers, it wasn't really necessary either, it was just For the Evulz.
In one encounter, Envy is about to be stabbed by Ling Yao, so it alters its appearance to that of Lan Fan, who has just been driven away to get medical attention for a severe injury she attained while protecting Ling, causing him to freeze up and enable Gluttony to swallow him. Brotherhood takes this a step further than the manga, having Envy appear as Lan Fan in her current vulnerable state; bandaged and without her left arm, her mask gone revealing a hurt expression.
Which makes no sense whatsoever, as Lan Fan was gone by the time Envy showed up, and it had only ever seen her with her mask on. And, unless it had met up with Wrath before going after Gluttony, it had no way of knowing that she had lost an arm, especially as Brotherhood skipped over Envy's role in it and Gluttony's fight against Ling and Lan Fan.
In Envy's fight against Mustang near the end of the manga: Mustang finally gets to confront Envy about who murdered Hughes. Envy responds by shape-shifting into Hughes' wife, and laughing at how easily he was tricked. Mustang is not amused. During the fight, they end up in some narrow corridors, and Envy take the opportunity to appear in Hughes's form. It does make Mustang momentarily flinch, but unfortunately for Envy, the whole reason Mustang was after it was because it had murdered Hughes, and the reminder only served to piss him off even more. It was a Curbstomp Battle to begin with, and that stunt only made things worse for Envy.
Hilariously, Envy is something of a Hypocrite regarding its use of this trope, referring to it as a cheap trick and taunting opponents when they fall for it, but then turns around and tries to invoke What the Hell, Hero? on the ones that don't.
Envy (To Mustang, while disguised as Hughes): What's the matter with you!? You didn't even hesitate to incinerate your best friend!?
During his climactic fight with Ed at the end of the 2003 anime version, Envy cycles through the forms of everyone who's been either hurt or killed as result of Ed's actions. He tries to psyche him out by turning into Dr. Marcoh, his mom/Sloth, Hughes, and Mustang (which only makes Ed attack him harder). For the most part it only makes Ed angrier (pointing out he killed Sloth when she tried it), and he even goads Envy into showing his original (human) form. Let's just say it was one family reunion Ed was not expecting, and the shock allows Envy to line up a fatal blow.
In One Piece, Mr. 2 Bon Clay uses this as a desperation attack against Sanji. Sanji heartlessly beats up all of the doppelgangers of the male Straw Hat pirates, and Bon Clay is about to give up till he carelessly switches to Nami, which paralyzes Sanji with lust. Bon Clay comments, "It can't really be that easy, can it?" He toggles his face-switching power on and off to cure his disbelief, and then uses the form of Nami against Sanji because Nami looks just too cute for him to hit. Until Bon Clay learns he can't use his Okama Kenpo properly because he's not used to her physique.
In Saint Seiya Lyumnades Kaza did this thrice on-screen (plus a couple off-screen times). First in a battle against Cygnus Hyoga, taking the form of Aquarius. Then against Pegasus. Then in battle against Shun by transforming into his brother; it didn't work at first. He did it again when Shun was getting the upper hand, and it made Shun doubt enough for Kaza to beat him. Finally he did it against Shun's brother Ikki by transforming into Shun. But as Ikki was a Genre SavvyAnti-Hero, it didn't work.
Better yet, Ikki beats Kaza by transforming into him, and Kaza whines that he's unable to hit his own image. This shows how cowardly he is,because this wouldn't have worked on any of the heroes.
In Bleach, the hollow Grand Fisher has a lure on his head. By reading his target's psyche, he can transform that lure into the person the target cares about the most. He impersonates Ichigo's dead mother early on in the series.
Later on, an Arrancar also impersonates Kaien Shiba, Rukia's mentor, to great effect. This particular one happened to be the 9th Espada, Aaroniero Arruruerie. In both cases, the impersonator had eaten the impersonate-ee.
Parodied in Ranma ½, when the Cat Demon possessed Genma, thinking that Ranma wouldn't attack him. Ranma's response: IT'S EXORCISM TIME!
To explain further, it really didn't help that Genma forced Ramna to fight a giant cat since, no matter how weak a demon it was, Ranma is utterly terrified of cats. Right before booting his son towards said terror, Genma says that it's a martial artist's job to defeat demons, no matter what. Ranma repeats that right before beating up his old man.
Dance in the Vampire Bund: One of the assassins sent after Akira in vol 4 pulled this. It worked perfectly when he took the form of Graham, a colleague whom Akira killed under as yet unknown circumstances, but then she(?) twisted the knife and tried to extract information by taking the form of Mina. Big. Mistake.
In Project ARMS, one of the cyborgs that Hayato fights tries to trick him by impersonating Ryo. In this case, it was done to trick Hayato and not guilt him. After Hayato figures out the truth and impales him, the cyborg takes the form of Hayato's dead mother before dying.
Dougan in the Saiyuki Requiem Movie absolutely adores doing this; so much so that it becomes pretty much the premise of the entire movie. For Sanzo he changes into his mentor Koumyou as well as his teammates Sha Gojyo, and Son Goku. For Goku he changes into Genjo Sanzo. For Sha Gojyo he changes into Hakkai and induces stabby death onto him. And for Cho Hakkai he shapeshifts into both his dear sister/lover Kanan as well as his friend Goku.
Various enemies try this in the Saiyuki manga as well. Usually to not much effect since the main characters can be positively gleeful about beating up doppelgangers of one another. On one memorable occasion they start beating up a doppelganger of Gojyo before realising it's not him (they did have reason to be angry with him at the time, though).
Fairy Tail: A variation of this is used by Monsieur Sol against Elfman in the anime. He used his earth powers to create clones of his dead little sister. Borders with horror.
Variation in A Certain Magical Index: The girl in the dress can make people feel in their hearts that she is someone else, usually a loved one. Shiage Hamazura is unable to attack her when she makes him feel that she is Rikou Takitsubo, his girlfriend. The girl in the dress notes that some people will attack her harder if she tries this, because by perceiving her as a loved one, they believe they have been betrayed and become enraged. When faced against Accelerator, she retreats, reasoning that the Ax-Crazy psycho would react that way.
This happens twice in the series' New Testament Vol 6:
Shizuri Mugino gets confronted by what seems to be Frenda Seivelun, who she had killed back when she was a bad guy and had been feeling guilty about ever since. "Frenda" orders her to atone for her sin by dying, then moves to attack her. At the last second, Mugino snaps out of it and fights back. Her hunch that it wasn't actually Frenda was right, it was a shapeshifting man who wanted to play on Mugino's guilt to weaken and then kill her.
Kakine Teitoku makes an army with his Dark Matter that looks, sounds, and acts like the Misaka Sisters and turns them on Accelerator. Accelerator, who had sworn to protect the Misaka Sisters and is eternally guilty about killing some back when he was a bad guy, falls into despair and almost lets them kill him. Mugino steps in and saves him. Drawing on her experience with the fake Frenda, she reminds Accelerator that they're just Kakine's puppets, not the actual Misaka Sisters, which restores his will to fight.
In Heaven's Lost Property, Chaos shifts in and out of the forms of Nymph's friends while beating her up and berating her. Nymph objectively knows that the being before her is Chaos and not her friends, but it doesn't matter, she's too traumatized to fight back. When Ikaros tries to attack Chaos, she shifts into Tomoki, and Ikaros is fooled even though she saw her transform before her eyes and obeys Chaos until Astraea intervenes. Later, when Ikaros is about to throw Chaos into the sea, Chaos turns into Tomoki again and begs her to stop, but this time, Ikaros points out that Tomoki is an excellent swimmer and wouldn't be worried about the sea.
In Neil Gaiman's The Sandman, Loki attempts to pull this on the second Corinthian, cycling through a series of forms (starting with Dream, followed by a dragon, the Corinthian himself* Corinthian's reaction: "Oh, please. Credit me with at least the wit to know which one of us I am.", the toddler who the Corinthian is supposed to be rescuing, a flame, and finally his true form) trying to find one the Corinthian won't strangle. The Corinthian, needless to say, is not impressed.
The Elementals by Bill Willingham did an elaborate variant which revealed that a Shapeshifter that the Elementals had fought before had, over the course of a Story Arc gotten one of the team, Morningstar, to fall in love with him/her.
A rare heroic example comes from Wild CATS. When team was fighting Lord Entropy, an impossibly powerful madman who wanted revenge against Lord Emp for killing his wife, Voodo used her illusion to look like her. Entropy was so confused that Emp ha enough time to prepare to wipe the floor with him.
Another heroic example in Runaways, when Xavin shifts into the late wife of a man-turned-monster to talk him down from his destructive rampage.
Astonishing X-Men: Subverted (and inverted?) in Joss Whedon's run. Kitty Pryde is confronted with Colossus (the genuine article); not believing it's really Colossus, back from the dead, she tells him that if he's a robot or a clone, she'll understand, but if he's a shapeshifter or illusionist, he's in for a new meaning of pain.
In Nodwick, the party encounters an undead monstrosity that uses magic to make whoever is looking at it see a dead mentor or parental figure they would trust implicitly (Nodwick sees his former guildmaster, Arthax sees the man who trained him to be a wizard, Piffany sees the head priest who raised her, and Rowan sees her adventurer father). All of them can only stare dead-eyed at it and mumble "I thought you were dead". Fortunately, while the magic also affected Orville, his species of dragon instinctively try to fight and kill their own parents for dominance...
Red Lantern Rankorr used his power ring to make constructs resembling Abysmus' victims, paralyzing him with guilt and allowing Atrocitus to defeat him.
Early on in Avengers: The Initiative, Trauma had difficulty controlling his fear-based transformation powers, causing him to freak out Cloud 9 by transforming into a zombified version of MVP, who was killed while protecting Cloud 9 from an errant rifle blast. When Hank Pym tried to intervene, Trauma transformed into an extremely battered version of Janet Van Dyne, reminding Hank of his domestic abuse incident, which sent poor Hank scrambling for his anti-anxiety meds.
An inadvertent version occurred when the Runaways visited Avengers Academy. Reptil tried to entertain the guests by showing off his dinosaur-transformation abilities. He made the mistake of turning into a deinonychus in front of Klara who, up to that point, still believed that she was responsible for Old Lace's apparent death, resulting in Karolina having to rush over and calm the poor girl down before her powers started kicking in.
In the Kingdom Hearts fanfic, A Match made in Hell, the Big Bad tried this separately on Sora, Roxas, and Pete, transforming into everyone they knew, including Organization XIII.
In the Chaos Verse (an official spin-off of the POV Series), the Big Bad Nightmare Phobia infiltrates Fluttershy's dreams and takes the form of her friends to try and drive her to suicide. It almost works, but thankfully, Fluttercruel is able to intervene and save her.
In Getting Back on Your Hooves: Checker does this to most of the Mane Six during the Final Battle, taking the form of their loved ones and giving them each a Breaking Lecture based around their personal faults and saying those faults have in some way harmed said loved ones. Special mention goes to Rainbow Dash's, which involves her how she handled Discord's Sadistic Choice, something she feels genuine guilt for.
In the Mortal Kombat movie, the villain Shang Tsung tries to pull this gambit with Liu Kang by assuming the form of his dead brother Chan, whom Shang Tsung had killed at the start of the movie. It doesn't work.
The monster in Phantoms turns itself into a little boy who looks like the kid Ben Affleck's character accidentally killed in his former life in the FBI.
The T-1000 from Terminator 2: Judgment Day made use of this trope, shape shifting into Sarah Connor in an attempt to lure and terminate her son John. The attempt fails when the real Sarah appears behind the T-1000, and John trusts her characteristic approach ("Get out of the way, John") over the duplicate's attitude of slumped defeat. The film's special edition, disappointingly, replaces this subtle indicator with an obvious shape shifting flaw (warped and misshapen feet).
Inverted in Dreamscape. Assassin Tommy Ray murdered his father as a teenager. While fighting him in a dream, the heroic Alex distracts him by changing his appearance to that of the father and asking Tommy Ray why he killed him.
In The Exorcist, the demon takes on the voice of Father Karras' recently deceased elderly mother.
In Event Horizon, the title ship has taken over Dr. Weir. In an effort to get to Captain Miller, Weir takes the form of a flaming Edward Corrick, the man in Miller's back story whom he had to leave behind in his greatest failure. Miller doesn't buy the attempt to guilt-trip him for a minute though: "No. You're not Edward Corrick. I watched him die."
Mystique tries this on her captors in X-Men: The Last Stand. She transforms into the President and threatens to have them all court martialed if they do not release her, and then a little girl who begs and cries to be let out. She finally turns mockingly back into herself when one of the guards threatens to empty a can of pepper spray in her face if she doesn't knock it off.
In Wrath of the Titans, Perseus fights and defeats a minotaur. As he's about to finish it off, the minotaur suddenly starts talking in his son's voice, begging his "father" not to hurt him. Perseus kills it anyway.
Older Than Print: In Arabian Nights, one story involves a hero being told that he must kill a demon that is taking the shape of his mother. He refuses, is sent back where he started, and has to undertake all the other challenges of the quest again, as well as kill the copy of his mother.
In the novel Myth-Taken Identity, a group of shape shifters are running around disguised as the protagonist of the series, and their chief uses it against the protagonist's mentor in the climactic fight.
Magic Time: There's a whole swarm of these towards the end of the final book, divided into groups targeting each main character. (For instance, a doctor who survived Chernobyl fights animated radiation corpses. What, the title made you think it was a kids' book?)
In Juliet Marillier's Child of the Prophesy, the Evil Matriarch Oonagh does this during the middle of the climactic showdown: while facing off her son and granddaughter, she takes on the appearance of the son's dead wife. Made worse by the fact that she killed the wife in the first place. This throws her son off-balance long enough that she would have killed him, had his half-brother not intervened.
A Boggart does this to Mrs. Weasley in Order of the Phoenix, tormenting her by transforming into an image of her children, dead. Comes true in Deathly Hallows.
In Perelandra, Ransom is fighting the Un-man (the demon-possessed undead corpse of Weston, the previous book's villain) when it suddenly reverts to Weston's actual personality and begs for mercy. Ransom ignores it, and the narration points out that Weston's actual soul had most likely been completely subsumed long before.
In a non-villainous example, Bartimaeus of The Bartimaeus Trilogy regularly appears in the form of Kitty Jones in the beginning of Ptolemy's Gate, purely because he knows how much guilt his master still feels over Kitty's apparent death in the previous book. He sometimes exaggerates the curves, though.
Ciaphas Cain (HERO OF THE IMPERIUM!) experiences this in one book: while on a raid on a Slaaneshi cult, he's quite surprised to see Amberley Veil (his boss with benefits), and can't bring himself to shoot her. In fact, hearing the soldier next to him comment in the same love-struck tones though with a different name, he is consumed by jealousy and about to shoot him. Fortunately Jurgen moves closer and dispels the effect, revealing her as the old brothel owner. "Impersonating an Inquisitor is a capital crime" indeed.
Live Action TV
An episode of Red Dwarf features a genetic mutant which uses its shape shifting ability to drive its victims to extremes of some emotion, which it then feeds on/sucks out. So at one point Kryton becomes the victim of a literal Shape shifter Guilt Trip.
The Supernatural Season 1 episode "Skin" does this when Sam fights a shape shifter disguised as Dean. Sam can't kill him, so Dean does.
Averted in Episode 5.05 "Fallen Idols" in which a pagan god is about to take the form of John Winchester and gets killed before that happens.
It happens again in Season six. When the boys prove unwilling to listen to her, The Mother Of All takes on the form of none other than Mary Winchester. Still doesn't stop the Winchesters from ganking her.
Subverted in an episode of Angel, when the Monster of the Week appears as Wesley's distant father and is unceremoniously shot. Notably this only happens after he threatens Wesley's love interest, and since Wesley did think it was his real father at the time he spends the next episode absent, apparently dealing with the revelation that he would have been willing to kill his own father. Made more humorous with all the other characters saying how they killed "their" fathers or mothers and haven't looked back since.
Although not done intentionally, the demon Illyria who has "hollowed out" and taken over the body of Fred notes that Spike has no problem punching her in the face.
Illyria: This shell... you had affection for it.
Spike: Tons. Loved the bird.
Illyria: Yet you strike at her form without sentiment.
Spike: You ain't her. I can see it. Lord knows I can smell it. And I got no problem hitting it.
Also done in the Doctor Who story "Planet of Fire".
On Heroes, Candace (who can actually cast illusions, but used it in a way equivalent to shapeshifting) as Simone to Isaac.
Notably averted on Alias. The heroes want to kill her extra.
The Worm creatures in Kamen Rider Kabuto occasionally do this by showing the image of the person they'd replaced. One early episode has a Worm guilt tripping Kagami with the form of his brother, noting that since the Worm has all the memories of his victim, if the Worm dies the victim will be killed "a second time".
It happens again in Kamen Rider Double's movie, Begins Night, in which a dopant poses as Shotaro's mentor and in turn, Kamen Rider Skull. When it is revealed that it's the Dummy Dopant doing the imitating, this pisses off Shotaro.
LOST: The Smoke Monster aka The Man in Black did this a lot to the main characters, though he was usually impersonating their beloved ones: he appears to Jack as his late father, to Eko as his late brother, to Ben as his late daughter, to Richard as his late wife... you get the idea.
The TARDIS inadvertently does this to the Doctor in Let's Kill Hitler, turning into each of the Tenth Doctor's companions in turn:
Worse, they do this right after the Big Bad apparently absorbs them both, leaving you to wonder just how fake it is.
Used a few times in a section of the first boss battle in Metal Gear Solid 4, with Laughing Octopus, who uses her OctoCamo and FaceCamo to disguise herself as Naomi, then as Metal Gear Mk. II, with Otacon's voice. When you approach it, it attacks you, with Otacon's voice (although obviously not him speaking) making fun of you. Of course you can spot the flaws easily (she never changes out of her suit when in the face cameo and MK II is much bigger then its normal size. Plus Otacan doesn't flag you down with it in regular play.)
You can briefly pull this off in Metal Gear Solid 3 thanks to Latex Perfection. Put on the Raikov mask and uniform when fighting his gay lover to distract him for a moment. "Ivan is that you?"
In Star Fox Assault, the final boss tries to pull this, although only with voices from the various people that died (or are presumed dead) during the storyline.
You can attempt one in Majora's Mask against Igos Du Ikana with his knight captain's mask. Then fail completely.
"Ohhh! Keeta! Is it not Captain Keeta?!?... But you're so... T-Tiny!!!"
Also done with the Gorman brothers of the same game while wearing their brother's mask, they get so upset looking at it they can't fight.
The Baldur's Gate series features dopplegangers and other shapeshifters who like to impersonate other characters, but all of them shift into their normal forms when attacking, thus disqualifying some interesting scenes from quite exemplifying this trope. The closest to actually qualifying are the random dopplegangers that attack you in the Candlekeep catacombs that appear in the form of familiar minor characters and speak lines that don't actually make sense for those characters but are still related to what they might actually say; the greater dopplegangers near the end of the level try to convince you that it's all been an illusion and you've actually been killing the people that the dopplegangers looked like, but they stop pretending immediately if you choose to fight them. Throne of Bhaal also has a similar scene where some wraiths have a go at Breaking You by Talking in the form of lost loved ones, but they too do it only before the battle is joined, not during it.
Not quite an exact use, but referenced: In Paper Mario: The Thousand-Year Door, when the Shadow Queen takes over Peach's body, Goombella tells you that no matter how much it looks like your friend, you can't think of it that way and just have to fight it.
The Holoprojection droid PROXY in Star WarsThe Force Unleashed uses it to his advantage several times. Going against Vader as Obi-Wan Kenobi or against Boba Fett as his father Jango does not guarantee him victory, but does confuse his opponent for a few precious seconds.
In the Wii/PS2/PSP version of the first game, Darth Phobos briefly adopts the appearance of Juno Eclipse to lure Galen into letting his guard down at the start of the fight. After you defeat her, she tries it again to stop you from killing her. It doesn't work.
In the beginning of the sequel, Darth Vader orders Starkiller to destroy a droid that looks like Juno Eclipse, but he can't. The game's novelization includes a scene where Starkiller is confronted by a Juno droid again, as well as droids of his friends and father, but this time he declares that dreams and memories have no power over him anymore and destroys them all. The Dark Apprentice destroyed his Juno droid and declared that he felt nothing.
Completely averted in Prototype. If Alex is discovered by the military, while shape shifted, the military will not hesitate to fire on him — even if you're in the guise of a respected commander, unarmed woman, or someone they wouldn't dare think about hurting otherwise. Hilariously, if you use the Patsy ability to accuse someone of being Alex, the poor sod gets gunned down with an equal lack of restraint.
In Metroid Gandrayda pulls one of these once you defeat her. First, she changes into Ghor, then into Rundas, then into Samus. The whole thing takes less than a minute, and the only sound that comes out of her mouth is a scream, but the message to Samus is clear: You couldn't save them from The Corruption, you couldn't save me from it, and you're not going to be able to save yourself. Your Days Are Numbered, Samus.
Dante's Inferno: Lucifer takes the shape of Dante, along with his form massacring innocent people in his grand illusions, to break the will of Dante's wife's soul, Beatrice.
In Final Fantasy Tactics Advance, the final totema attempts this in a cut scene. It changes from Ritz, to Doned, to Mewt (all characters with a close relation to the main character), and then finally to the main character himself, each one trying a different tactic to try to get him to stay in the world and not destroy the final crystal. None of it works, though it does succeed in briefly mind fucking the main character.
Similar to the above, in Tactics Ogre The Knight of Lodis, when you enter the Very Definitely Final Dungeon, the first battle has Shaher attempt this on Alphonse and Eleanor, and who he takes the illusion of depends on the route you take. If you take Path A, he becomes Rictor, Alphonse's commander who was possessed by Shaher and subsequently killed by Alphonse. If you take Path B, he takes the form of Cybil, who felt she could no longer trust Alphonse and was later possessed by Shaher in a similar manner of Rictor in Path A. However, Alphonse doesn't buy it one bit, and simply lashes out at them and causes the illusion to break. Then again though, Shaher did actually say he would take their form to their face, but to be fair, even before he said this, Alphonse wasn't buying it.
In Fable III, after having to leave behind your mentor Walter in the deserts of Aurora, the demonic Crawler taunts you with illusions of Walter begging for help and being brutally killed by the Crawler's shadow monster minions.
In the Full Motion Video game Dracula Unleashed, Alexander, Helsing and Harker confront a friend turned vampire Juliet. They chase her back to her crypt where in a last ditch effort to save herself, changes into Harker and Alexander's wife and fiancee respectively. Harker sees through the guise but Alexander, apparently forgetting that that they're dealing with a supernatural force, nearly falls for it before Helsing stops him.
In Starcraft II Heart Of The Swarm, Anti-Hero Kerrigan faces-off against Shape ShifterNarud/Duran. The first tactic he uses is to shapeshift into Jim Raynor, which causes Kerrigan to hesitate for a quick moment, before having her Berserk Button pushed and beats up Narud mercilessly. Near the end of the fight, Narud shapeshifts into Kerrigan before she was infested, which causes her to hesitate long enough for him to stab her.
In God of War: Ascension, Kratos starts strangling Tisiphone and then she transforms into Lysandra, his wife. He hesitates for a moment, then continues.
In Spec Ops: The Line, a heavy trooper with an automatic shotgun "transforms" into Lugo, who was killed about an hour prior. Keep in mind nobody in this game has supernatural powers; the whole scene is Captain Walker's hallucination. He's guilt-tripping himself.
Question 13: Shape Changers You're in a fight against a group of super villains, and one of them is a shape-changer. Suddenly, your dead girlfriend shows up in her underwear. Do you: A: Ignore her. It's possible that your girlfriend climbed out of her grave, changed into her panties, and got on a plane to see you during a fight, but it's probably the shape-changer, genius.
In the Ben10 episode "Permanent Retirement", Ben is beating the tar out of one of the evil aliens (already posing as Grandpa Max) as Wildmutt when it shapeshifts to close up its revealing wounds and says in Max's voice, "Now, you wouldn't want to hurt old Grandpa Max, would ya?" Ben-as-Wildmutt hesitates, allowing the alien to start wallopping him and forcing Gwen to have to remind him of reality.
Gargoyles: In "The New Olympians," Proteus irritates the prison warden Taurus by taking the form of his father (whom Proteus murdered) and begging to be released from jail.
When the Superman copy is about to be destroyed by Superman, it turns into Lex and says "This Is the Part Where... you kill me, right?" causing Superman to hesitate long enough for it to (almost) turn the tables.
The Flash and Batman aren't affected: the Flash drone's attempt to Hannibal Lecture him fails miserably, and Batman defeats his double before it could open its mouth.
Flash's is particularly amusing, as him being aware of his heart of the team status and playing it up is what allows him to ignore his double's words.
Green Lantern and Hawkgirl are at first hounded by their doubles, but, having gone through a nasty break-up, decide to switch partners and take the opportunity to "let out some steam".
Wonder Woman's copy doesn't even speak, but she and Superman take a cue from the ex-couple and trade sparring partners, ending with them smashing their doubles into each other.
During "Endgame" of Transformers Animated, Shockwave tries this on Bulkhead and Bumblebee, asking if they're really willing to take out their old friend Longarm by changing to his form. (In this case, he's only sort of playing head games, as Longarm and Shockwave were always the same person. The Autobots feign sympathy for a minute before smacking him up.
An inversion appears during a Story Arc of the animated series; a Brainwashed and Crazy Morph shapeshifts into Wolverine's most hated foes (including Sabretooth and Omega Red), trying to take advantage of Wolvie's fractured and tormented memories of said foes to drive him to insanity. Unfortunately for him, Wolvie's got plenty of experience with repressing those memories, and he only escapes by taking advantage of the one memory Wolvie can't repress: being forced to leave Morph to die after a semi-botched mission.
Prior to that, he shapeshifted into Wolverine's unrequited love interest Jean, and mocked him about how she'll never love him.
Similarly, Mystique shape shifts into Ms. Marvel to dredge up a bad memory in Rogue of her past to try and guilt her into abandoning the X-Men and hook back up with her; the memory was of Mystique ordering Rogue to fully absorb Marvel's powers and personality, an action that caused Marvel to pop up on occasion as accusatory hallucinations. Rogue eventually had to ditch Mystique as a result, joining the X-Men and having Professor X block her mind of Marvel and the incident to keep the hallucinations at bay, but since he was at this time MIA and unable to keep the block in place, Mystique was trying to convince Rogue that she was the only one in the world who could help her with it.
In Sym-Bionic Titan, the main trio fights a chameleon monster that tries to do this, notably impersonating Octus' girlfriend Kimmy. Octus is fortunately, reminded that it's not really her (especially as the mutraddi's eyes are pretty much its own).
Gravity Falls has a variant in the episode "Into the Bunker"—after being shoved in a Cryo Prison, the Shapeshifting monster tells Dipper that he will never find the Author, and that if he keeps trying, "this will be the last form you'll ever take." It then transforms into a copy of Dipper, screaming in pain, as the freezing takes effect.