The phrase "cast spell on" implies the use of magic or supernatural powers to influence someone or something. Antonyms for this phrase could include "disenchant," meaning to remove any magical or enchanting influence, or "repel," meaning to ward off or resist any influences. Other antonyms could include "release," meaning to free from any imaginary or supernatural control, or "untangle," meaning to clear someone's mind from any confusion or mesmerization. Alternatively, use of logical argument or persuasion could provide a direct contrast to the idea of casting a spell. Synonyms and antonyms can be important tools for nuance and depth in communication.