Animagus

An Animagus (pl. Animagi) is a witch or wizard who can transform themselves into an animal and back again at will. It is a learned skill, unlike the hereditary skill of a Metamorphmagus. Information on Animagi is taught to Hogwarts students during their third year Transfiguration class. Animagus registration exists to keep track of those that have learned this skill.

Getting the skill
It takes skill, practice, and patience for wizards and witches to become Animagi. The process of becoming an Animagus is long and arduous and has the potential to backfire and cause the transformation to go horribly wrong. Many witches and wizards simply feel that their time might better be employed in other ways, as the skill is of limited practical use unless one has a great need for disguise or concealment. Part of the process by which one becomes an Animagus is holding the leaf of mandrake in their mouth for an entire month, using the leaf for the creation of a potion, reciting an incantation (Amato Animo Animato Animagus) on a daily basis[2], and drinking the Animagus potion during a lightning storm. Once the initial training is over, an Animagus can then change at will, with or without the use of a wand. Animagi who take on the form of species capable of flight can enjoy the sensation without the need of broomsticks, flying carpet, or riding on flying animals.[3] It is debated (but generally believed possible) for one's Animagus form to be a magical creature, and also debated (but generally believed impossible) for an Animagus to be a dementor. The process is extremely difficult and can result in disaster (such as permanent half-human, half-animal mutations) if done incorrectly. A witch or wizard must keep a single mandrake leaf in their mouth for an entire month (from full moon to full moon). If the leaf is removed or swallowed, the witch or wizard will have to start over again. At the next visible full moon (if the night happens to be cloudy one will have to start over) the wizard must spit the leaf in a phial within range of the moon's pure rays. To the moon-struck phial, the wizard or witch must add one of their own hairs, a silver teaspoon of dew that has not seen sunlight or been touched by human feet for seven days, and the chrysalis of a Death's-head Hawk Moth. The mixture must be put in a quiet, dark place and cannot be in any way disturbed.