Your Shapeshifter character is, for whatever reason, having trouble keeping it together mentally — so their form switches around in accord with their mental tribulations. The shapeshifter's base identity — who they are to begin with — is in danger of getting permanently lost in the mental jumble and resultant physical manifestation of every shape they have ever taken happening at random, on provocation, or if the wind changes.
May be triggered as a result of Becoming the Mask, or may result in Becoming the Mask if you have a Manipulative Bastard guiding the person back from the crisis point. It can also be due to The Mind Is a Plaything of the Body, as having many different forms can make determining which one is the "real you" a bit more difficult.
If the shapeshifter does not survive the crisis, then it's a Shapeshifter Swan Song. If the shapeshifting happens involuntarily due to being sick or some rare condition to the shapeshifter's race, it's Malfunction Malady instead.
Subtrope to Power Incontinence.
- The fate of "Copycat" Ken at the end of the Ranma ½ episode he appears in. His copied forms start to bleed together and he is left begging for help in making it stop. Played for Laughs, obviously.
- Majin Tantei Nougami Neuro features a really horrific villain whose motivation for his murders is this. He has an out-of-control Healing Factor that allows considerable shapeshifting but also means all of his cells are constantly replicating at horrific speed, ''including his brain cells'', so he has no idea what his proper form or sex or name or anything are, and his early memories are long since lost.
- He's really pathetic. You feel sorry for him in spite of all the things he's done. Of course, then the real Big Bad turns up and sorts him out...
- In the Wild Series, all manbeasts lose control of their form when in extended contact with humans, losing their sanity and attacking them. This is traumatic for the manbeasts themselves, who don't harbour any ill-will to humans.
- Haiyore! Nyarko-san has this in the flash anime Remember My Love(craft-sensei), with Nyarko's cousin Nyarue. Tends to happen when embarrassed. And considering them... That's a problem. (Though it's censored to protect audience sanity.)
- Chameleonians in Space Dandy, who don't even know their true forms, are believed to suffer from this. Even if they don't, they can make their imitatees question which is real one.
- Fantastic Four:
- The entire race of Poppupians are an inversion to this trope. They exist naturally in a state where they have no solid identity and switch fluidly and easily from shape to shape. Their natural state is to identify more or less as each other, so they don't really have a base identity to lose or worry about getting back.
- Delirium, the personification of madness in The Sandman, sometimes transforms involuntarily into multicoloured butterflies or fish.
- Chameleon (of the Spider-Man rogues gallery) has ended up like this at least once. He realized that he didn't have an independent identity anymore - just a big collection of faces stolen from his enemies. So he ends up in an asylum, switching continuously from one identity to the next, desperately searching for a face to call his own...
- Captain Britain's lover Meggan in Excalibur had this in personal relations at times; her limited shapeshifting became more responsive to her empathy the closer she became to someone. Even the form she most often took (beautiful, blue-eyed, busty blonde) was a response to falling for Brian Braddock at first sight. But she also would shift to look more like Colossus or Nightcrawler if she was bonding with them.
- In Ms. Marvel (2014), this happens to Kamala when she first gets her powers; left in a state of confusion, she transformed into her hero, Carol Danvers, and thus wound up taking Carol's old "Ms. Marvel" title.
- In Adventure Time: Marceline and the Scream Queens, one shapeshifting character has changed forms so many times he not only can't remember what he originally looked like, he can't remember his real name. He tries to pass himself off as a variety of different were-creatures, with his "true" form being a nondescript human man with the name Guy - as in, "guy who can shapeshift".
- One Young Avengers fanfic involves this. After being ambushed while on holiday, Wiccan comes home to reveal that he can no longer use his magic and that Hulking "is gone", with the obvious implication being that he's dead - the fic's Arc Words being "Teddy's gone." It takes a year for Tommy to realise the truth and confront Billy with it - that Billy was the one who died in the attack, and Teddy has been using his shape-shifting abilities to live Billy's life in his stead (his reasoning being that the world in general had a lot more to lose from Billy's death). By the end of the fic, and throughout the follow-up, Teddy seems to genuinely believe that he's Billy, and that it's himself who died - his grief prevents him from accepting the truth, and he ends up Becoming the Mask.
- Mister Nobody, from the Wild Card series, was trapped in the form of King Kong for nearly thirty years before someone realized that, since apes are immune to the wild card virus, the Giant Ape had to be an actual person inside that form. He was rescued by the telepathic Doctor Tachyon, and has since got his life together for the most part.
- In Animorphs #35, Marco can't deal with the stress of his father marrying his math teacher (because he doesn't realize that Marco's mom isn't really dead), so he starts to morph Mix and Match. A similar plot occurs with Rachel in #12 (with Involuntary Shapeshifting), although this is due to an allergic reaction.
- This is part of Tobias' ongoing struggles: he gets Shapeshifter Mode Locked as a hawk in the first book, and by the third he's already starting to forget what he looked like as a human. Fortunately this is alleviated a little by his human friends, as well as the fact that he eventually regains his human form, albeit only for two hours at a time.
- An early example happens in Harlan Ellison's short story, "All the Sounds of Fear", in which Stanislaviskian actor Richard Becker, famous for becoming his roles and avoiding the limelight personally, goes insane and starts to become each of his roles again, going backward. At one point, when he switches from one role to another, we're told that his face seems to almost physically shift. And at the end after he's been his first role again, we get our last glimpse of him in a cell at the asylum, screaming "Give me some light!" over and over again, his face an eyeless blank.
- Inverted in Harry Potter—Tonks was unable to shapeshift through most of book 6, because of her extreme stress that she's in love with Lupin.
- In Galaxy of Fear Hoole is against using a permanent fake identity.
"To a Shi'ido like me, identity is everything. I must always remember who I am. Otherwise, with all the shape-changing I do, I am in danger of forgetting who I really am."
- Whateley Universe: In All Hallows Ball: Part 3, Steve Rossiter talks about Chaney Syndrome:
It's named after the actor, Lon Chaney, the so-called 'man of a thousand faces'. This, and he gave a gesture to indicate himself, isn't what I look like.
Lina shrugged. So, what do you look like?
Steven shrugged and stared at the oval rug the couch was sitting on. I dunno. I'm a shifter four. I can only do mammalian bipeds or quadrupeds and I only have this much mass, but otherwise I'm any body. He rapidly shifted, sex and appearance, movie stars, TV News Anchors, Presidents, then was back to the blonde teen paragon. That's what Chaney Syndrome is. If you can be anybody, who are you?
- In This Is Not A Werewolf Story, Raul's mother has been Shapeshifter Mode Locked as a wolf for several years. Near the end of the book he begins to worry that her human mind has faded away since then, noting, for example, that she doesn't seem to understand what people around her are saying.
- Raul arguably starts to fall into this himself when he gets stuck for a few months. When he meets his father partway through that time he notes that this is the first time in a while that he's started thinking in words.
- A Villainous Breakdown version happens with Sylar from Heroes. The already mentally unstable serial killer with Parental Issues gains shapeshifting and begins cycling back and forth between his mother's form and his own as he has a conversation with himself via what he thinks she'd say. This eventually leads him to write 'I AM SYLAR' in blood at his next murder scene as he desperately tries to hang onto who he wants to be.*
- An interesting version occurs in an episode of The Flash (2014). After spending the entire episode impersonating various people before finally being caught, Hannibal Bates is finally apprehended and imprisoned. Wells notes that they've seen Bates become a lot of people...but never himself and asks him who he is. Bates' response? "I...can't remember.".
- In supplemental materials, Cisco attempts to help Bates remember and he responds negatively to it. He apparently doesn't want to remember.
- The Flanders and Swann song "The Chameleon", ends:
"If that chameleon were me, I'd be ashamed to sham.
Each night, all white, between the sheets
I'd wonder who I am."
- In Aberrant, Turncoat was initially an agent of the Directive, an organization that distrusts most novas and recruits only those with low-key powers, or those that can be used for subtlety. After infiltrating the nova-supremacist Teragen, he slipped rapidly into their belief system despite his initial intentions. As part of the story of "When Heaven Ends", the last of the canonical adventures, he accidentally transforms into someone who is covertly scanning him, believes himself to be that person, and runs off just in time to escape the colossal battle his actions helped set off.
- The Big Bad of Phoenix Wright: Ace Attorney Dual Destinies is "The Phantom", a spy who is so adept at impersonating others that his original identity has long been lost even to himself. As such, when blood evidence is finally discovered tying him to his multiple crimes, he starts to break down because he has no idea who the "him" that would be caught is! This results in him tearing off mask after mask, desperately trying to find his true face. Just as he tears off his last mask, he's shot by a sniper, and his body falls in such a way that his face (and only his face) is obscured by darkness.
- The Blank, from the Global Guardians PBEM Universe, is a shapeshifting teenager who can make himself... or possibly herself... look like any human. She... or perhaps he... has lost track of his... or is it her... original gender and appearance. The fact that her... or is it his... real name is "Leslie" (one of the few details of his... or is it her... original life that she... or is it he... remembers) doesn't help matters.
- This comic from Brawl in the Family has Kirby copying other characters who can copy other characters, eventually turning into Deku Link while saying, "I don't know who I am anymore...."
- The "Ballad of G.I. Joe" is a surprisingly downbeat look at the cast on their off hours, and it suggests that Zartan, Cobra's mercenary Master of Disguise, is on the fringe of this.
- X-Men: Evolution Rogue already has mental instability problems due to her mutant copycat power generating copies of the minds and personalities of those she touches. After touching Mystique and acquiring her shapeshifting (and discovering the latter is a Magnificent Bastard manipulator) shapeshifts into various heroes and villains she's touched, in response to things said to her or people she encounters.
- Iron Man: Armored Adventures: Whitney Stane's Madame Mask mask becomes the vehicle for the same sort of shapeshifting switcheroo when the technology powering it gives her brain damage, resulting in Sanity Slippage.
- In Mighty Orbots, Bort suffers from this due to his lack of self-confidence and ongoing identity crisis.
- In Batman: The Animated Series, Matt Hagen was already in crisis before Roland Daggetts goons poured Mutagenic Goo on him and turned him into Clayface. Once transformed, the former actor believes his life is over until he starts to reminisce on his past movies and begins involuntarily shapeshift into his past roles. Naturally he decides to use his newfound power to seek revenge on Daggett but in the process he starts to become more unstable and aggressive, even violently lashing out at his best friend. In the end, Batman knocks Clayface into a room of televisions featuring pictures of his past selves. His shape shifting goes berserk.
- This is what drives the SpongeBob SquarePants episode "Mimic Madness". After learning that imitation is the sincerest form of flattery, SpongeBob starts doing impressions of everyone he talks to, shapeshifting from the chest-up into a yellow spongey version of whoever it is. After doing over 80,000 impressions, Sandy, Mr. Krabs, Patrick, Squidward and Plankton arrange for an intervention, but after doing an impression of all five of them simultaneously, SpongeBob runs far away after trying and failing to be himself. Then he vents this in song.