As the power of an evil creature increases, they become more of a large, disfigured abomination -- until they cross the Bishonen Line, beyond which as they gain more power, they (re)gain humanoid form. On some cases, this could also be viewed as the creature being Functional Genre Savvy. For example, a huge monstrous abomination cannot physically participate in the impressive martial arts stuff that a Fighting Series is built around, so if it's in one of those, it gains an advantage by reverting to a humanoid form that will fare better Kung Fu Fighting. Examples of Bishonen Line include: