After losing a match against Evolution in 2003, the "Big Red Monster," Kane, was forced to permanently remove his trademark red-and-black mask. This resulted in audiences seeing his true face for the first time since the character's debut 6 years earlier - despite allegedly having been severely burned in a fire, Kane's face was not covered in scars as he claimed; he was simply that insane. Now that he could no longer hide his "disfigurement", Kane became even more psychotic and dangerous than before.
Japanese pro wrestling loves this trope. Jushin "Thunder" Liger, during intense rivalries, sometimes transforms into the more aggressive, much more evil looking "Kishin Liger". Also Bx B Hulk, a normally upbeat gimmick about dancing, turns into "Killer Hulk", adopting an all black costume and evil looking facepaint.