The phrase "has down pat" is often used to describe someone who has mastered a particular skill or task. However, there are several synonyms that can be used to convey the same meaning. These include being proficient, skilled, expert, seasoned, accomplished, adept, and knowledgeable. Other similar phrases might include having a firm grasp on, being on top of, or being well-versed in a particular area. Whatever phrase you choose, the idea is to express the notion that someone has a thorough understanding of a given topic or skillset and can perform it with great ease and accuracy.