Muck up is a phrasal verb that means to spoil or mess up something. One antonym for "muck up" is "fix," which means to repair or put something in order. Another antonym is "enhance," which means to improve or make something better. A third antonym for "muck up" is "succeed," which means to achieve a desired outcome or goal. Lastly, the term "perfect" could also be considered an antonym, meaning to make something without defects or flaws. It is important to know antonyms for words like "muck up" to better communicate in various contexts and text.