Mix in is a common phrase used to describe the action of adding ingredients to a mixture or combining two or more elements. However, there are several synonyms that can be used instead of mix in to add variety to your writing or speech. Some examples include blend in, incorporate, intermingle, fold in, stir in, meld, integrate, combine, and fuse. These synonyms can be used interchangeably in various contexts, whether it's cooking, music, or even interpersonal relationships. Whatever word you choose to use, make sure it accurately conveys the concept of combining two or more things together seamlessly.