Daily Chinese Idiom Guessing Game
To change one's identity or appearance suddenly and completely, often in a surprising or deceptive way.
旧时神怪小说中描写有神通的人能用法术一晃身子就改变自己本来的模样。现用来形容人不讲道义原则，一下子来个大改变。
明·吴承恩《西游记》第二回悟空捻着诀，念动咒语，摇身一变，就变做一稞（棵）松树。”
The ordinary-looking man shook his body and changed into a police officer, surprising everyone.