Mean Makes You Hideous

Mean Makes You Hideous is a term used often to describe a phenomena in which a character becomes increasingly hideous the more he/she dwells in the antagonistic side or dark side, be it the result of becoming mean or evil in his/her own volition or external corrupting influence or both. Not all mean characters are evil because they often considered neutral characters.

Like He Who Hunts Monsters, the term of a character whose appearance become increasingly hideous the more he/she commits evil acts or submitting oneself upon corrupting influence or even both has been populared by two separate articles of TV Tropes: Evil Makes You Ugly (where the character become increasingly repulsive appearance) and Evil Makes You Monstrous (the character's deformation not just on appearance, but also have personality that warped as worse as the appearance), but is technically did not originate on that website.

The term actually originated from various folklores, legends, and myths in real life about horrific consequences from committing 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; anyone who dare to commit such crime doomed to become a Wendigo themselves.

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

Marvel Cinematic Universe

 * Red Skull: According to Erskine, why Red Skull become extremely evil and having deformed face is clarified due to imperfect Super Soldier Serum revealed the very monstrous side of him: Before his disfigurement, Red Skull already had negative qualities and power hungry traits to begin with, opposed to Steve Rogers a.k.a. Captain America who only gained super strength but retained his good qualities since he was already good guy from start.

Star Wars

 * Practitioners of Dark Side of the Force: Practicioners of Dark Side of the Force such as Palpatine would suffer deformation the longer they embrace the Dark Side, where the said deformation started from simply having yellowish eyes. But from there, it could get worse where the skin would become pale and fill of wrinkles, though this is not always the case.

Anime and Manga

 * Apostles: Apostles are said to be humans who have sacrificed their humanity, dreams, and loved ones to turned into monstrous demons with a Behelit.

Western Animation

 * Barraki: The Barraki were turned into their monstrous forms when they fall into the ocean, which was happened to have mutagen due to Kanohi Ignika's power.
 * Umarak the Hunter: To begin with, Umarak was already evil and selfish as he not truly loyal to Makuta as he followed the latter for convenience only. That is until dons Mask of Control where his evil nature grows, resulting him also become more like a hideous monster.
 * Blight: Even prior to his mutation into Blight, Derek Powers already evil from start. He killed his own employee Harry Tully in cold blood to test his invented nerve gas and later, murdered McGinnis who learned about the gas and make it appear the latter was the victim of The Jokerz gang. Even so, he failed and made McGinnis' son, Terry, who learned about his corrupt ideal with help of elderly Bruce Wayne, becoming a new Batman and stopped his evil plan to sell the gas. However, in ensuing fight, Derek wind up exposed by his very created gas and to make matter worse, radiation treatment that meant to save Derek's life mutate him into monstrous creature with glowing transparent flesh and black skeleton.

Live Action Films

 * Jason Voorhees: Being supernaturally enhanced to monstrous killer that can resurrect himself via electrocution, each demise and resurrection that Jason had, combined with his persistence to kill more victims resulting in him becoming stronger and monstrous over time. A testament of his evolution into more hideous killing machine was after blown into bits, his strong drive to kill more people somehow allowed him to return as parasitic worm zombies after only his heart that survived destruction of most of his body parts.
 * Freddy Krueger: Thanks to his deal with nightmare demons, the restless spirit of the child killer Freddy Krueger, who was evil from start, transcended into an undead dream-dwelling human monster.
 * Chucky: As a killer doll, he started off as cute looking doll, but it is obvious that due to his bloodlust and evil personality, the look of his doll form become increasingly hideous due to his doll vessel slowly mutating from plastic to actual flesh and blood.
 * Theodora: After being manipulated by her older sister Evanora into eating a magic green apple, Theodora transforms from a kind, young, beautiful woman into a green-skinned, wicked witch more evil and malicious than her own sister.
 * Evanora: After having her magical necklace accidentally broken by Glinda, Evanora transforms from a stunning, beautiful young woman into an old, wrinkled and ugly hag; her true form.

Animated Film:

 * The Evil Queen: For wanting to be the fairest in the land by killing her stepdaughter, when the Queen decides to take matters into her own hands, she first concocts a potion that transforms herself into a hideous old Witch and spends the rest of the movie in that disguise.
 * Gaston: Despite being extremely handsome on the outside, Gaston is ugly on the inside and becomes even more uglier when Belle refuses to marry him, along with realizing that she loves the Beast instead of him.
 * Mother Gothel: Invokes to Rapunzel about the dangers about the outside world. However, Gothel fits in this trope as she uses Rapunzel's magic hair to keep herself young and beautiful, but once Flynn cuts Rapunzel's hair, Gothel immediately ages uglier than ever before leading to her breakdown and demise.

Television

 * Demons (Supernatural): It was clarified that demons started off as damned souls who were corrupted through extensive torture in hell.

Videogames

 * Sorceress Power wielders: It was said that anyone who inherited the Sorceress Power would have physical changes which reflect on their personality traits: Had they become evil, their Sorceress power would resulting them taking more monstrous appearance. If they remained good, their physical change will not make them hideous.
 * inFamous series established that the state of a conduit (offshoot of human race with superpowers)' powers and physical appearance reflected that of their morality and mental condition; the eviler and/or unstable they are, the more hideous and destructive their powers and appearance can be. This was shown through Sasha whose physical features became less human as the result of mental instability from her obsessive love and fallout with Kessler which worsened after exposed to Ray Sphere explosion by the time Cole MacGrath confronted her, leading to the latter worried the same thing will happen to him.
 * Ironically, Cole will suffer physical deformation as worse as Sasha the more he uses his powers for evil and selfish reason, which reflected through his dark red electricity as opposed to his heroic self's light blue one.
 * Joseph Bertrand III's power to turn himself and others into insectoid monsters is allegedly not as hideous as it seemed had he not rejected and used it for his genocidal campaign against Conduits.

Comic Books

 * Judge Death: Judge Death, Judge Dredd's undead nemesis, was already evil and sadistic due to sadism that his father taught to him. Death spent his whole life killing people before allowing a pair of witches to turn him and his three lieutenants into undead abominations to achieve immortality. Since he was already pure evil long before his transformation, casting off the last of his humanity means the outside simply started to reflect the inside.

Literature

 * Lord Voldemort: Harry's encounter with partially corporeal form of a piece of Voldemort's soul that come from his diary and later revelation by Dumbledore about the Dark Lord's past revealed that Voldemort used to be very handsome, but his meddling with dark arts began to deformed his looks that, upon his rising to power that schemed through manipulating Triwizard Tournament, his restored form looked more like a horrifying humanoid creature with snake-like nose and skull-like face compared to his former appearance.
 * Mr. Hyde: Due to Mr. Hyde being dark aspect of Dr. Jekyll's psyche given form where the doctor would take hideous appearance whenever Mr. Hyde takes control, it is not surprising that Mr. Hyde emerges as monstrous creature.
 * Gollum: After he killed his own friend, Deagol, to get the One Ring, over time, was transformed by it into an ugly Hobbit creature.
 * Beauty Smith: Due to his hideousness, he became a cruel and abusive dogfighter so he could fit in with society.