The term fiendish is employed by writers to evoke a sense of diabolic mischief or dread, often imbuing characters or actions with an almost supernatural wickedness. Its use ranges from describing a laughter that is as delightfully sinister as it is unnerving [1] to depicting the eerie glow of malevolent eyes that seem almost possessed [2]. In some narratives, fiendish characterizes not only physical expressions—a grin or a leer suggestive of inner malice [3]—but also schemes and cruelty that betray a deeper, calculated wickedness [4, 5]. It can further accentuate the atmosphere of a scene, transforming an ordinary action into something unexpectedly dark and perilous, as seen when a motor-cycle hurtles by at a fiendish speed [6] or when a character’s rage becomes fiendish in its intensity [7, 8].