Evil Makes You Hideous

Evil Makes You Monstrous is a term used often to describe a phenomena in which a character not only corrupted on the inside due to outside malevolent force or turning to the dark side, but also on the outside where the more he/she become evil, the more hideous she become as well.

Like He Who Hunts Monsters, the term has been populared by TV Tropes, but did not originate on that website. The term actually originated from various folklores, legends, and myths in real life about horrific consequences should one commit a horrible crime/evil act, often as punishment of their actions. For instance, in Native American mythology, legends about cannibalistic monster named Wendigo is the warning about act of cannibalism, where should one performed act of cannibalism, the said person would turned into another Wendigo as well.

In many stories, heroes may warned by his parents/friends about horrific consequence of literally turned into monstrous creatures as punishment of specific crime or other evil acts.