It was a horrible sound. The most horrible sound Kryten had ever heard. Crunching bones and sickening wetness, and a scream that dipped all the way down to Hell.
Lister stopped being Lister and started to become something else. His body folded in on itself, and when it re-emerged, it was inside-out. The slimy, mucus-coated organs quivered and gurgled as the ribcage split open and a strange suction-like head slithered out and began sliming across the floor towards Kryten's feet.
— Red Dwarf: Better Than Life
Transformation Horror is a subtrope of Body Horror involving graphic and unsettling transformation sequences (not the trope) or continuous random mutation.
This can occur in the process of both Involuntary and Voluntary Shapeshifting, and the final form, if there is one, doesn't have to be horrific. Even turning a person into a Ridiculously Cute Critter can involve Transformation Horror along the way. What matters is that the process of the transformation is unpleasant to witness, and horrifying just to imagine experiencing.
There are several standard forms of Transformation Horror:
- Mutation Horror: Slowly accumulating chaotic mutations. The victim gradually becomes increasingly twisted and deformed due to the growing influence of The Corruption, exposure to nuclear waste, Mutagenic Goo, or The Virus. There is no "end form", only ever-increasing levels of Body Horror usually involving asymmetric and chaotic changes and tumorous growths. This variety tends to end in either death, Face–Monster Turn, or the victim's best attempts at screaming.
- Horrifying Metamorphosis: Slow Transformation into a known end form. Often part of the Viral Transformation process or a particularly unpleasant form of Metamorphosis or Forced Transformation. The victim experiences a disturbing, slow change into their new form. The end result does not have to be body horror, but the process of adopting an entirely new body plan is likely to involve quite a bit of body horror.
- Traumatic Transformation: Rapid Transformation into a known end form. Some transformations condense all the horror of a targeted slow transformation into a brief, squicktastic Transformation Sequence. Often emphasizes the face and visibly reshaping skeletal structures, and is usually accompanied by the sounds of popping bones and rearranging organs. Nearly always painful or disorienting. Common in Darker and Edgier Animorphism: The transformation of a werewolf, for instance. note
- Terminal Mutation: Targetless and Fast. A particularly nasty Cruel and Unusual Death involving rapid degeneration or mutation until death. See Rapid Aging, I'm Melting!, and Shapeshifter Swan Song for just a few of the possible causes. Examples of this form should be placed on their respective pages unless they are particularly noteworthy as transformation horror as well.
- Mix And Match Mutation: Sprouting Combat Tentacles or a Shapeshifter Weapon can be disturbing enough, but when more and more are added to the mix you have the recipe for a Shapeshifter Mashup. Even more horrifying if it's involuntary, such as in the case of Power Degeneration, or an Adaptive Ability going totally haywire.
There are several layers of reasons why people find this trope disturbing:
The most obvious is that transformation can be very Squicky: even in the case of one human becoming another human, facial features and major bone structures have to distort and rearrange. This naturally means that the course of a transformation tends to at least pass through the Uncanny Valley at some point, and quite often takes the scenic route.
Transformation also invokes the fear of losing control of your own body, or having it turn against you: Transformation Horror is unusual among the fantastical forms of horror in that adults fear it almost as much as children do because it has so many parallels and examples in Real Life. Puberty, unexpected changes in people around us, the ravages of old age, slowly losing one's own identity to mental illness, or worse, having a loved one turn against you, are all too real events experienced by most people at some point. All it takes to make horror from them is exaggeration. Even more extreme forms such as Mutation Horror or Terminal Mutation invoke our fears of disease and decay; in a sense, this trope is why we find diseases like cancer, rabies, leprosy, and the bubonic plague exceptionally terrifying: they transform a victim physically and mentally from the inside out.
Not all transformations are necessarily horrific; this trope can be averted in any number of ways. Lighter and Softer universes tend to have relatively tame transformations leaving any disturbing elements to the imagination. On the other hand, in Darker and Edgier universes, even Voluntary Transformations tend to be traumatic for everyone involved and depicted in all their disturbing glory. The medium can have a huge bearing as well: distortions that would be Nausea and/or Nightmare Fuel in live-action can be fairly innocuous in a cartoon.
The causes and circumstances of the transformation can make a difference as well. A character slowly turning to stone can be fairly mild visually, but played for Psychological Horror; an otherwise disturbing transformation can be mitigated when it's the result of a character Cursed with Awesome activating their Lovecraftian Superpower or receiving a Power-Upgrading Deformation.
An example of how this trope can be intentionally both invoked and averted is the Transformation Comic genre, with various comics averting this trope for fanservice or comedy, playing the trope straight as Fan Disservice to maintain a serious tone, or even alternating between the two.
Compare Clone by Conversion, Transflormation, Viral Transformation, Painful Transformation, Slow Transformation, Transformation Sequence, Transformation of the Possessed, and Transformation at the Speed of Plot which often overlap.
Compare and contrast Forced Transformation, which sometimes overlaps with Transformation Horror. The distinction is that the victim of a Forced Transformation has become something else against their will, while Transformation Horror is about becoming something else in a disturbing way. Eldritch Transformation often combines these two and exaggerates them.
Contrast Nothing Is Scarier and Fridge Horror for transformations that aren't actually shown/described, and Teleporter Accident for similar things happening instantaneously. Bit-by-Bit Transformation can be used both to subvert this trope by spacing out the squick into tolerable doses, and to exaggerate it by combining Horrifying Metamorphosis and Mix And Match Mutation.