What is an amimagus?

Answer 1

Amimagus is the opposite to a wherewolf. A wherewolf transforms into a wolf in the event of a full moon, and the time there isn't any full moon it is human. The amimagus is a wolf which transforms into a human when it's full moon.

Answer 2

An Animagus is a witch or wizard who has the ability to transform themselves into an animal at will. This transformation is different from a normal Transfiguration spell, as it is a skill that requires practice and dedication to master. Each Animagus has a specific animal form that they can assume.