Metamorphmagus

A Metamorphmagus is a witch or wizard in the Harry Potter continuum who can change their appearance at will. This ability is very rare, with the series containing only two Metamorphmagi: Nymphadora Tonks and her son, Teddy Lupin.

The Metamorphmagus ability has some level of genetic heritability, shown by Teddy. However, neither of Tonks' parents were Metamorphmagi.

Due to their canonical rarity, any original character who is a Metamorphmagus in a Harry Potter fanfic is very likely a Mary Sue. As such, being a Metamorphmagus is frequently a charge.

"Metamorphmagus" is a proper noun in Harry Potter, and the first "M" should always be capitalized.