An Animagus (plural: Animagi) is a wizard with the ability to metamorphose at will into the animal that best suits his personality, but he cannot know the form he will take until the end of his apprenticeship. Learning to be Animagus is very difficult and requires several years of learning. It is for this reason that the Ministry of Magic monitors very closely those who want to become one.

Process:
Becoming Animagus is the result of a complex process, consisting of ten steps:
Keep a mandrake leaf in your mouth for an entire month (between two full moons). This sheet should never be swallowed or removed from the mouth. If the leaf is taken from the mouth, the process must be restarted.
When the full moon comes, remove the leaf and place it, bathed in saliva, in a small crystal vial exposed to the moonlight (if the sky is cloudy that night, you will need to find a new mandrake leaf and renew experience). Add to the flask one of your hair and a silver spoon of dew collected from a place that has not been exposed to the sun or stepped on by man for seven full days. Finally, add the chrysalis of a Skull Sphinx to the mixture and place it in a dark and calm place. Be careful not to look at it or disturb it in any way until the next thunderstorm.
While waiting for a thunderstorm, follow the instructions below at sunrise and sunset. Place the tip of your magic wand over your heart and say the following incantation: Amato Animo Animato Animagus.
The onset of a thunderstorm can take several weeks, months or even years. Throughout this period, your crystal vial should remain calm and be kept out of direct sunlight. Exposure to the sun will cause the worst possible mutations. Resist the temptation to go check out your potion until the storm hits. If you conscientiously repeat the mantra morning and night as described above, you will eventually experience a second heartbeat when you point your wand at your chest. This beat may be more or less intense than the first. Would not change a thing. Continue to repeat the incantation at the appointed times, no matter what.
As soon as the first lightning appears in the sky, go immediately to the place where you hid your crystal vial. If you have followed the steps above scrupulously, you will find a blood red potion there.
Go immediately to a safe and large enough place where you can proceed with your transformation out of danger and out of sight. Place the tip of your magic wand over your heart and say the incantation Amato Animo Animato Animagus, then swallow the potion in one gulp.
If everything went as planned, then you will experience severe pain and your heart rate will be twice as fast and intense. The form of the creature you are about to become will take shape in your mind. Don't tremble. It is now too late to escape the transformation you have desired.
The first transformation is usually painful and frightening. Your clothes and everything you wear (jewelry, glasses) merge with your skin to turn into fur, scales or thorns. Stay calm or your animal instincts will take over and do something stupid (like attempting to leap through a window or run headlong into a wall, for example).
Once your transformation is complete, you should regain your ease. We strongly recommend that you pick up your wand and put it in a safe place, where you can easily find it when you return to human form.
To do this, form as precise a mental picture as possible of your human body. That should be enough to trigger the transformation, but don't panic if it doesn't happen immediately. Over time, you will be able to switch from your human form to your animal form at will - just by visualizing the creature in question. The most seasoned Animagi can transform without the aid of their magic wand.