The first step for becoming an Animagus was that the witch or wizard in question had to keep a single Mandrake leaf in their mouth for an entire month (from full moon to full moon). If the leaf was removed or swallowed, the witch or wizard would have to start over again.

At the next visible full moon (if the night happened to be cloudy, one would have to start over) the wizard had to spit the leaf into 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 had not seen sunlight or been touched by human feet for seven days, and the chrysalis of a Death's-head Hawk Moth. The resulting mixture then had to be put in a quiet, dark place, and could not be disturbed in any way.

The next thing that had to happen was for the wizard to wait for an electrical storm, whenever that might be. During this waiting period the wizard would have to, at sunrise and sundown everyday without fail, chant the incantation Amato Animo Animato Animagus with the tip of their wand placed over the heart. When, at last, there was a lightning storm, the wizard had to move immediately to a large and secure place, recite the incantation one final time, and then drink the Animagus potion.