(last updated: 12/28/17)While the majority of people in the world are generally humans with perfectly mundane lives and lifestyles, things can very easily break down in the fighting world. In the underworld and fighting tournaments alike, rumors abound of monstrous fighters who are not simply wearing costumes or using trickery--but legitimate beasts, men and women whose bodies have become warped beyond all recognition. These types of people are certainly almost always fighter class, as the sort of happenstance that can transform a body is also the sort that a human would not normally be able to survive.
Most of the time, these forms are attained by "conferred chi." This is a sympathetic effect of a person's body naturally forming a harmony with the chi around it. Blanka is the most well-known example of this--his body naturally became attuned to the chi of the Amazon rainforest after spending his entire childhood there, taking on the properties of many of the jungle animals that he encountered there.
While a monstrous form does not always infer any great strength, many creatures with metanatural forms do possess some uncommon ability or trait that reflects their savage nature, such as Blanka's ability to electrify his skin, learning the talent from the electric eels he'd seen in the river.
As stated previously, an altered form is most often the result of some accident with--or prolonged exposure to--a particular potency of chi, as in Blanka's case. However, a person's body may just as easily be born with a natural disposition towards a particular type of chi; enough exposure to the chi in question might be the cause for a metanatural form. A fighter with a natural affinity for cats might acquire one or two cat characteristics simply by keeping the company of other cats. More extreme examples typically require generations of extreme exposure. A disposition of chi can be inherited from one person to another in certain cases.
However, sometimes people are afflicted with some illness of the chi that abruptly causes them to take another form. These forms are usually more subtle and less detectible, but not always. Lycanthropy, an affliction often involving a hypersensitivity to the moon's distant chi, often causes rampant shapeshifting in those afflicted by it. Other afflictions such as vampirism are more of a debilitation than a boon, requiring victims to constantly reinvigorate themselves with the chi of others to continue living. Many fighters have died of these types of afflictions, and it takes a very strong and disciplined individual to properly harness them; such people tend to be highly isolated simply because of their rarity.
The last category of metanatural forms are the internal change. There is no disease or environmental factor that caused them to assume their form. This is the basis for the mythological belief that a man who kills enough people will become a demon; a great warrior can become so strong that his or her body naturally twists and mutates itself to fit his or her ideals and personality. It is noted that this is only achievable by fighters of a very high ratio: Many of history's greatest warlords were known as monsters or gods for this very reason.