Shapeshifter Identity Crisis

What happens when your character with Voluntary Shapeshifting begins to suffer Sanity Slippage?

You get a Shapeshifter Identity Crisis, which is the sometimes non-lethal sibling to Shapeshifter Swan Song, and the polar opposite of Shapeshifter Mode Lock.

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.

Anime and Manga

 * The fate of "Copycat" Ken at the end of the Ranma One Half 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...
 * You wonder how, though. He's basically a giant lump of cancer somehow managing to function as an organism. Sicks controls this enough to give her a base form and identity how?
 * I think it's mostly psychological. And likely full of lies.
 * 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.

Comic Books

 * 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.

Literature

 * 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 so he starts to morph Biological Mash Ups. A similar plot occurs with Rachel in #12 (with Involuntary Shapeshifting), although this is due to an allergic reaction.
 * 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,
 * Tonks in Harry Potter stopped changing her appearance and became ordinary-looking and mousy-haired in response to.

Live-Action TV

 * 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.

Web Original

 * 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.

Western Animation

 * 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.
 * In the original cartoon, when Morph first returns from the dead, he's in bad mental shape, and thinking of his "former" friends tends to result in him unconsciously taking their forms.
 * 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.