The phrase "freak of nature" is often used to describe something that is unusual or abnormal. However, there are many synonyms you can use to express the same sentiment. A few examples include: anomaly, aberration, oddity, monstrosity, rarity, eccentricity, quirk, aberrancy, deviation, and variation. Each of these words carries a slightly different connotation, so it's important to choose the right one for the situation. For example, "anomaly" suggests that something is unexpected or doesn't fit the usual pattern, while "monstrosity" implies that something is grotesque or repulsive. Experiment with these synonyms and see which ones work best for you!