Something which is in the mix can mean to be in the mixture as in a component of something. In the mix can also be used to describe an addition to an existing group or collection of things or being in competition or in the running for something.

1. The boxer's fantastic win last night has put him in the mix for a title shot.
2. Although the book sold well, the author was disappointed that it was not in the mix for any of the major awards.

1. Our new offerings are luxury products with a few affordable offerings in the mix.
2. We felt our team was lacking a creative perspective so we hired a creative director to add in to the mix.