There are several synonyms for the phrase "good genius," which refers to someone who is exceptionally skilled or talented. One alternative is "mastermind," which implies that the individual in question has a high level of intelligence and expertise. "Prodigy" is another option, highlighting the person's exceptional abilities from a young age. "Wizard" is a synonym that invokes the idea of magic and mystery, underscoring the person's unique talents. "Savant" is often used to describe someone who has a remarkable skill in a particular area, such as a musical savant. Finally, "genius" itself is an appropriate synonym, emphasizing that the individual is exceptionally gifted and talented.