Fatal smile is a mysterious and enigmatic expression that possesses the power to captivate and attract people, but also can be lethal or lead to a disastrous outcome. Some synonyms for this phrasing could include a deadly smirk, a lethal grin, or even a dangerous smirk. These terms all convey the same idea of a smile that may evoke a sense of danger or lethality. More alternatives include an ominous or malicious smile suggesting something unnerving or malevolent. The concept of a fatal smile is widely used in literature and media, often representing a character's dark and sinister motives or intentions.