There are many synonyms that can be used for the term "most mastered", including accomplished, mastered, proficient, skilled, expert, adept, expertly, proficiently, and skillfully. All of these terms indicate a high level of mastery or expertise in a particular area or skill. The term "most mastered" specifically implies that the subject has reached a level of mastery that is higher than others in the same field or subject area, and that they have achieved a level of proficiency that is worthy of recognition and admiration. No matter which synonym is used, these terms all convey a sense of excellence and expertise in one's chosen area of focus.