Mutation

Mutation is a term used in genetics to indicate the modification of a human being. Contrary to the Transmogrification or the Shapeshifting, it is not had to the Magic or a power. But by the science. It is undergone and irreversible. Vampires, Werewolves, certain demons like Skilosh Demon and Wraith-er Demon or the rite of the Ascension have the capacity to infect and/or to convert by bite their victims. In this case, it is similar to the demonic Possession and not a mutation. Human psychics, seers and telepaths like Drusilla, Cassie Newton, Agnes Bellfleur...are not mutants. Their abilities, although that has no magic origin, are mystic. In the Buffyverse, there are two types of mutants.

Scientific Mutation

 * Gill Monsters were the result of steroids administered by Coach Carl Marin on Dodd McAlvy, Cameron Walker, Gage Petronzi and Sean Dwier. He managed to find the solution to old Soviet Experiments on the DNA of fish such as tarpon and mako shark to improve the performance of Olympic swimmers. Even though the formula was successful on the Sunnydale High Swim Team, extended use eventually led to the boys transforming into large, humanoid fish-like monsters. When transforming, the person's skin would completely shed off, leaving a mindless beast with a taste for human flesh and the capability of breathing both underwater and on land.
 * Pete Clarner concoct a potion in order to increase his strength and virility, though it also mutated him into a clawed monster. Initially, Pete required to drink the formula to transform, but eventually its effects became triggered by anger.

Innate Mutation

 * Dr. Ronald Meltzer was a brilliant surgeon with the power to sever and reattach his body parts, over which he had some sort of telekinetic control (he can levitate them in the air) thanks to his mastery of psychic surgery after being inspired by a book about how everyone was connected to the world around them due to them sharing molecules. It is possible that this capacity was innate, but only revealed by the reading of the book.
 * Bethany Chaulk is a young woman with telekinetic powers. Bethany's father sexually abused her when she was younger, which caused her to develop her powers. Her mutation is possibly innate, but only revealed after her bad treatment.
 * Gwen Raiden is born with the ability to generate and manipulate electricity, though the source of these abilities remains a mystery.
 * "Radie" was a slang term for human beings who have been mutated by the Sun's radiation in the future. These mutations were hereditary, so even those not directly affected could inherit them from their parents. Radies like Loo, Jove and Amma were relatively commonplace in the 23rd Century, at least in the city of Haddyn. Gunther was an example of a radie, his mutation taking the form of a fish-like physiology which required him to live underwater to survive.